I posted impressions in the random talk thread! In short it's a better Wii. If you don't like the Wii, then, uh...at least for PS3 sports, there is less waggling and wrist movements. Ping pong feels like ping pong and it really does track the position of it in the room. There are no real video games for it yet, so you aren't losing out on much unless you love the sports simulators. The hardware itself is nice, but the battery life and charging time sucks (internal battery, so you can't swap) and the glowing ball gets annoying.
Originally I was planning to hold off until there were more games, but the kmart deal was good, so I decided to pick it up. Haven't tried the navigation sub nunchuck controller and I don't think any games use it yet.
For what it's worth, if you do like the sports simulator stuff, ping pong is really good. Unlike the Wii, you really do need to do full motions on the higher difficulties; if a ball is coming to the left, you literally need to either jump to the left in real life, or do a back hand shot to reach it. If you want, you can even walk closer to the TV and play the net.
best news from the entire experience: the new time crisis lets you play with the PS Move or Guncon3. I can finally play something othe than TC4 with my dusty GC3

I've heard Table Tennis is fantastic and the technology is good. But the games are just Wii fodder
pretty much this