Playstation Vita games are 500mb to 3.5gb right now, will go higher down the road
Army Corps of Hell / Ridge Racer is about 500mb-600mb each
Uncharted Golden Abyss is about 2.8gb
Blazblue Continuum Shift Extend is about 3.2gb
Oh, and each time you put in a new PS Vita game cart, it installs stuff on the flash or the memory card. Basically a boot-up app. It's there even if that specific cart isn't there on the vita but it deletes everything if you remove it from OS screen. Not sure if it'll remove trophy datas (before sync) but i know you can only have 100 games / apps listed, including trophies listed locally, at least for now.