I also turned my Captivate back in for an iPhone 4. Reasons:
1. I also have spotty GPS issues.
2. The battery is OK, but is spotty. I spend most of my days texting, checking email, and having some internet use. The battery will get to 50% in 4 hours one day and last 80% the other. I check my battery usage and the vast majority (60%-70%) is on the display. This is with screen brightness all the way down.
3. Gmail integration is great, but the default mail application is complete dogshit.
4. Somehow Samsung decided to leave out the option to sync only my contacts, not all contacts. No, I don't need the "show contacts with phone numbers" workaround because I have email contacts without phone numbers I wish to retain. When I first synced up my phone, it pulled every single person I ever emailed into my address book. After cleaning it out, it still adds every person I emailed to my address book. Unfortunately I tend to update numbers/emails and add people frequently so I wish to keep it constantly synced to gmail, but that simply won't work here.
5. Colors. Who's bright idea was it to make everything in Android customizable except font sizes and colors, and more importantly, make the SMS theme with pacman colors? The default mail application isn't much better. Also, I don't see the point in having a 4" screen when everything uses 24 point font, so a line of text takes up 1/5 of the screen anyways.
There's a lot of things right about android (the notification system, google googles, google talk application, 720 video camera, the integration of all apps into contacts and google), but there's just enough broken with it to make me want to return it. 90% of my phone usage is texting and email, and when those basic features are inferior to the iphone 4's, then i'm going to switch.
Android customization is nice but I also don't want to have to play with my phone all day to get it set up to something usable. Yeah, linux is great, but it's also too much of a hassle to use on a regular basis.
Sure, maybe this will all get fixed in September by samsung and with Froyo 2.2. However, I'm not willing to roll the dice on being stuck with the phone as it currently is.
Another key factor in my decision is availability and resale value. A NIB captivate sells on ebay for around $400. A mostly new iphone4 fetches $600+ easy, so if android 2.2 does come out and the captivate becomes awesome, I can always sell my iphone and get the captivate.