I love my iPhone 4. I even have it out here at my desk with me as I surf the net, even though I don't need to have it right now, as it's 3 am and I'm not exactly expecting anyone to call... but I've only had it a few weeks and I'm still in the honeymoon stage of wanting to play with it all the time. That stage lasted a good six months with my 3G, and I expect it'll last even longer with my 4.
I like Facetiming with my fiance when he's working late - we'll FT while he's in the office doing paperwork, ect - not for long, just ten or fifteen minutes, but it feels so much more personal than just a phone call. It is seriously a cool thing, even with the wifi limitation. I'm lucky to live in SF where there's lots of free wifi, so I like to think I'm not that limited.
I love the camera - photography is a hobby of mine, and even though I try to take my DSLR with me as much as possible, sometimes it's just not convenient. It's nice to have a decent camera on me all the time. Love the HD video too - it's fun
Retina display is gorgeous
battery life is fricking amazing
it's kind of hard to get bored with an iPhone cos there's always new apps coming out
in conclusion: the iPhone rocks
I'm not an Apple fangirl btw - I dislike Apple computers, and love my PC. But Apple has a way with small handheld devices - what can I say? I loved my iPod back in the day, and I love my iPhone.