TweetDeck solves the syncing issue by requiring a TweetDeck account in addition to the Twitter account. Signing up is quick and painless. I downloaded the application on my iPhone and signed up for a TweetDeck account that way. It only required an email address and password and I was ready to go. I grabbed the most recent release of TweetDeck for Mac and plugged in the account information I set up, and syncing took place automatically. It is a very slick process and one that will definitely sway me away from Tweetie as my iPhone client of choice.
If you're comfortable with TweetDeck as a desktop client, the iPhone client will look immediately familiar to you. By default there are 3 columns-- All Friends, Mentions, and Direct Messages. You can swipe through these panes quickly and easily, in a pretty intuitive way. Like most other iPhone Twitter clients, you can select an individual tweet, and through that tweet you can reply, direct message, re-tweet, forward or add it as a favorite. You can also select the Twitter user and get more information on the user. Tweets can include photos from your camera or photo library, and can include your location. In this day and age of competitive iPhone Twitter applications, this is a pretty standard feature set.
Performance on the iPhone is pretty good, but certainly not perfect. I had a couple app crashes during my testing, and even when successfully launched it would sometimes be a bit sluggish moving from column to column, and screen to screen. I reviewed this app on my original iPhone, so I'm hoping the additional horsepower the 3G S offers will solve some of the stability and slowness issues.
I love the syncing between the desktop and iPhone client, but TweetDeck is not my perfect solution, especially on my Mac desktop. The deck takes up my entire screen with its 3 columns, and looks very "un-Mac." There are weird inconsistencies with TweetDeck on my Mac compared to other applications (due to its Adobe AIR cross-platform underpinnings); for example the preferences panel is nowhere to be found in the standard menu bar. Instead it is located in a small "wrench" icon at the top of the screen. The scroll bars are very different than on any other application I use. Overall, the desktop client just feels like it doesn't belong on my Mac in the way that Tweetie does.
Similarly, the TweetDeck iPhone client tries very hard to match the look and feel of the desktop, despite it not really "fitting in" with the look and feel of the iPhone. On my iPhone I prefer a light background and dark text, so it fits in with the look and feel of most other iPhone applications. TweetDeck looks noticeably different than most applications, which could be considered good or bad depending on who you're asking.
All that being said, I love the "shake to refresh" option, but that may just be because I am very easy to please. Both the desktop and the iPhone client are able to update your Facebook status if you choose.
The price for both the iPhone and desktop client is very hard to ignore -- TweetDeck is a free download for both the Mac and iPhone client.