Couple of things that jumped out at me that I appreciated;
1. user reviews - again a very useful feature in determining which sites will warrant investigation is the "authority" feature.
2. advanced searching features - the ability to search blogs by Boolean search strategies - or thru browsing how the blogs themselves have tagged their areas of coverage.
3. self tagging - really liked the way I could assign tags to my blog to bring users interested in particular issues (in my case libraries, information science, and internet technologies).
As for some of the results I obtained while searching - I found that using "learning 2.0" as a search term - even an exact term - didn't reveal that many hits from our blogging experiment. A tag search with the same term revealed a lot more hits - along with a revelation that there were some busy bees that have already finished the 23 things in an explosion of impressive effort ;)
And my own humble batgirl blog? Well let's just say that after sorting through pages of search results (with the optional authority limiter set to "any authority") I was still only able to find my blog using the "blog search" feature in advance search mode - and with the limiter of "fresh" blogs... I guess it has been a bit naughty - but still under visited! Hopefully registering in with Techorati will change that in the future. hehe