In case you missed TUAW Podcast #24, I've gone gaga for Philip Dow's Journler. It's a phenomenal donationware app that offers robust features for keeping a diary, storing files you need to keep track of, recording audio/video entries and even blogging. One of Journler's cruxes, however, is that its UI for tagging entries wasn't quite up to par; tags were separated with spaces or commas (your choice), but aside from searching, there was no decent way to really grab hold of and utilize your tags.
Fortunately, a beta posted by Dow in the Journler forums offers a glimpse at how the app's tagging paradigm is changing for the better - much better. As you can see, tags are now 'officially' recognized by Journler, and pressing return invokes a satisfying blue bubble around them, securing their entry in Journler's database. As you work with these new tags, Journler will also begin to auto-complete them, saving you more and more time as you continue down the path to Journler goodness.
[Update: I didn't even realize this, but Dow built in an even cooler, killer feature with these tags - you can click on then in an entry or in the entry browser and view a list of other entries using that same tag. I'm in love.]
If you decide to check out this new version though, be sure to read through the entire forum post. Dow had to make some changes to the way Journler stores and creates your tags, so he had to create an AppleScript you only have to run once to help get the new version up to par and convert over all your old tags for the new system. Naturally, you should back up your Journler folder in Application Support before trying any of this, but I happily performed the upgrade with nary a bump on the trip.
Don't forget: Journler is donationware, and Philip Dow sure would appreciate a few bucks for his excellent work.