It really depends on what it is. For a while I was desperate to upgrade my 3G, but then I got a new battery and now I have around 20hours battery life, and I don't really want video. If it has WiFi, then its very likely I'll get it.
Same here I have a 3G that I wanna get rid of, but I need a extremely good reason to. I mean photos and videos are nice but 6G has to be way beyond just that for me to wanna make the leap. If it can be an iPhone without the phone, with a good price, I'm probably in. If it's even better I'm getting it as soon as I can, which won't be too difficult because I live in NYC.