I've barely touched my PS3 since I got my Vita :-O, I'm not sure why either :-/, I think maybe when I turn on my PS3 I feel I have to commit, I don't really get that feeling with the Vita, it's like a portable PS3 that I can just pick up and play at my leisure, turning on the PS3 involves me turning the system on, then the TV, then the amp, positioning yourself into your 'gamer pose', it's kind of a ritualistic process to commit yourself and time to a video game, I'm not always prepared to put myself in the mindset.
Yeah, I'm experiencing the same thing. I love that I can play it on-and-off as I surf the web, cook dinner or whatever. If I didn't use it to watch movies, I could probably go months without booting up my PS3. It's a nice system but it's hard to spend time with it over the Vita.
On a similar note, I used a dualshock for the first time since I got my Vita and the analog sticks really threw me off. They felt so huge.