I own both a PS3 and ATV2 setup in the same room. Ever since I got the ATV2 I only use the PS3 for the occasional PS3 game or Blu Ray disc. The ATV2 is better for Netflix streaming and basically any other type of streaming.
One problem with using the PS3 for Netflix is that it is too loud and too power hungry to keep powered on all day. So when you want to watch Netflix you have to wait a while for it to power on, sign in, and the when it accesses Netflix there is quite a long wait before you can actually browse the content. The ATV2 on the other hand is "instant on" just like other iOS devices. Furthermore, when you click on Netflix it jumps to the content almost immediately. There isn't really a Netflix loading screen like you get with other devices. Quality is similar if not slightly better on the ATV2. The ATV2 is significantly better at catching onto the highest quality HD feed better and holding onto it throughout the stream. On the PS3, I notice it downgrading to a lower quality sometimes for short periods and it definitely takes longer to initially lock onto the HD stream.
Airplay is just awesome. I use it all the time with various apps including Vevo, Air Video, PBS, CNN, Youtube, EyeTV, iMovie, Photos, Safari, Photos and iPod apps, Pandora, and others. If you own an iOS device this is worth the $99 all by itself. Gives you more value out of the stuff you already have.
The other features about Apple TV that I enjoy are the easy access to all your movies, tv shows, music, iTunes U, and podcasts. All your content in iTunes is available on your tv and with Airplay, Home Sharing, and the free Apple Remote app you can access it all on your iOS device and even switch it back and forth between your mobile screen and any of the ATV connected TVs in the house at will with just the tap of a button. And no matter where you rent or buy iTunes content (iOS device, ATV2 itself, Mac, or PC) you can always watch it on your big screen TV with the ATV2. And of course you can rip your DVDs and Blu Rays and play them on the ATV2 too using iTunes Home Sharing. Handbrake is your friend. ;-)
Also, actually playing the content on the ATV2 just plain works far better than the DLNA solutions you have to use with the PS3 and I have tried them all. The stability, rewinding, fast forwarding, metadata support, playback controls, and user interface are all simply superior on the ATV2 compared to using DLNA on the PS3.
But like I said earlier, the PS3 is still awesome for full console games and playing Blu Rays from Netflix. Together they make a great combination. Each device does excellent what the other does not do well or is not capable of.