First off, I installed Google Desktop on a 2.16 GHZ Intel Core Duo MacBook Pro with 2 gigs of RAM. The app is Universal but I no longer have any PowerPC Macs, so I couldn't test its performance on one. Installing Google Desktop is as easy as you would expect it to be: download the DMG, open it, and double click the icon to install. However, the application that launches when you double click that icon is also new. It is the Google Updater, your one stop shop for all Mac Google apps. The Google Updater gives you the opportunity to download and install Google's other Mac apps (Google Earth and Picasa Uploader) while you wait. Frankly, I could do without installing a special application to download other applications. I realize that developers want to have more control over your entire experience with their apps, but these download managers can spiral into a Kafkaesque maze of downloading apps that only allow you to download other apps (I'm looking at you, Adobe). That's a road that Google would be best off avoiding.
Once you have Google Desktop installed it starts to index your computer's content. My past experience with Spotlight's indexing led me to believe that I should just walk away from the MacBook Pro for a few hours while the indexing was happening. Luckily, however, Google Desktop does a great job of indexing in the background while you continue to work away on your Mac (I don't know about you, but I'm a very busy industry pundit).
Once you start to work with Google Desktop you notice all the nice touches that Google's Mac developers have incorporated into it. Have you set up Spotlight not to index certain files (that's the list of locations under the Privacy tab in Spotlight's preferences)? Google Desktop won't index those files either. Want to save precious Dock space? Google Desktop gives you an option to display it in the Dock, in your Menubar (which I am using), both, or neither.
But that's enough of the window-dressing, how does one use this app and, more importantly, why use it over Spotlight? Activating Google Desktop is as simple as clicking on the icon in the Dock or Menubar (if you choose to display them) or by hitting the default hot key: Command, Command (that's hitting the Command key twice in a row). You can change the hotkey combo if you like, but for my money the default combo is very natural.
Once activated, a Google Desktop search box appears on your screen awaiting input. It starts searching as soon as you enter text, and displays the results in a friendly dropdown menu (though Spotlight's results dropdown is a little better organized). You then have the option of seeing all results (if they all couldn't fit in the drop down) or to search the web. If you choose to see all the results Google Desktop launches your default browser and presents your results in the very familiar Google results set webpage. Worry not, though, Google Desktop is not sending off your search results to Google HQ. The page, and results, are all produced locally (no need to fashion a hat out of tinfoil just yet, unless it is a good look for you). The results, as you can imagine, are sortable by relevance and date (the most recent files are shown first by default). Google Desktop also lets you look at the results that are just emails, web history, files, media, or 'other.'
Thanks to the way that Google Desktop works, it can even search files that you have deleted from your system. Google Desktop creates a cache on your machine that holds information about the various files that it has indexed. I created a test document that simply said 'tuawrocks,' a phrase that was no where on my computer before I created this file. Both Google Desktop and Spotlight immediately found the file when I searched for the phrase 'tuawrocks.' I then deleted the file, emptied my Trash, and searched for 'tuawrocks' once more. As you would expect Spotlight informed me that there were no files that met my criteria, but Google Desktop had a cached version of the file that I was able to look at (much like Google's web cache that allows you to look at websites that have gone offline for whatever reason). A very powerful feature, indeed, though one that could conceivably lead to a full hard drive. Luckily, you can tell Google Desktop not to keep cached copies of deleted files, though it would be nice if you could tell it to only keep x amount of deleted files in cache, perhaps in version 1.5.
Google Desktop's killer feature is integration with Google's other offerings, specifically Gmail and Google search. When you visit Google.com with Google Desktop installed you'll notice a new search option called 'Desktop.' This is a link to the local Google Desktop search that is running on your Mac. But it doesn't stop there. When you do a search at Google.com it is also searches your Mac's index for relevant results. Once again, privacy lovers fear not: you can turn this behavior off in Google Desktop's preferences.
Integration with Gmail is also a boon for all those who use Gmail (like yours truly). Enter in your Gmail account info, and Google Desktop includes all of your email in the results. It also caches your Gmail email locally, so that it remains searchable even if you are offline (but who is offline these days). Truth be told, this is a great feature, but it didn't actually work for me. I'm not sure if I just didn't give it enough time to index my email, or if something else is afoot. When I searched for things I know are in my Gmail account (like my name), Google Desktop did not find them. Your mileage may vary, but I was a little disappointed in this feature. I'll give it some time to index before I write this feature off (and I'll update the review with my findings).
Finally, many people often complain about Spotlight's speed. When I first ran Google Desktop I was sure it was returning results faster than Spotlight did for the same search. I went so far as to time a few searches, and both apps returns the results in comparable times (sometimes Spotlight had the edge, while other searches were faster in Google Desktop). Google Desktop certainly feels faster to me, though I imagine that is just a function of the way Google Desktop draws the results panel (and this opinion may be unique to me).
Overall, Google Desktop is a worthy addition to any Mac. Does it trump Spotlight? Well, Spotlight has a lot going for it. It is built into the OS, developers can build applications with hooks into it, and there is no need to install anything to get it working. That being said, if you use Google's full suite of products, Google Desktop is the desktop search for you. The integration with Gmail and Google.com is killer.
Google Desktop for Mac Score: 7.5/10
Pros: Works as advertised (for the most part). Integration with other Google services. Very responsive. Able to recover deleted documents. The price is great (free).
Cons: Need to use download manager to install. Not integrated with the OS. Gmail searching didn't work for me (if it did the app would have garnered a 9 out of 10).