People who have no problems rarely pour over iPhone forums posting comments. A lot of people might have little problems and not even realize it because they are just not that big of deal. Most people only ever post because they have problems - or because they want to start a fuss. That is why it will look like there are so many problems even when there are not.
There have been 2 million iPhone 4 sold, and maybe 4 or 5 sites have discussions about problems, and on those sites its mostly the same people posting the same junk over and over instead of actually having helpful troubleshooting and analysis.
Here is my experience with two pre-launch-day iPhones.
1. I was not able to duplicate the death grip problem, but I believe it does exist. I believe that firmware updates will improve this, but not cure it completely (I am not talking about changing the signal bars display - that is simply to help people understand better when they are in poor coverage, I am talking about improving how the radio in the phone handles the signal issues when the antenna are bridged) I also believe that in real world use it will end up impacting almost no one. Our signal reception has been great, and the only time we have been traveling outside of good signal areas with our 4 - we didn't have any problems with signal. I think it is simply way way way overblown.
2. I have had a bug when you do a "reset all settings" on the phone, it screws up the available options for "passcode lock" times. This is not an iPhone 4 problem, it is iOS 4, and happens on the 3GS as well when using iOS 4. The bug has been accepted and verified by Apple which means it will be fixed.
3. If you port a number from another carrier, FaceTime may not work. Apple released a knowlege base article with a solution, which resets FaceTime with your correct number and solves the problem. Probably will be completely fixed with the first software update.
4. AT&T has had problems with the new radio in the iPhone 4 which is HSUPA enabled. In some AT&T markets that use a particular network hardware - any device (not just the iPhone 4) was causing problems with the HSUPA. AT&T has disabled HSUPA in those markets and is working with the hardware vendor on a fix which will be deployed soon. This did not affect all AT&T markets.
5. Bluetooth connectivity in iOS 4 has been fairly unstable. Apple is looking into the bugs. I believe this is a problem with iOS 4 as it also seems to affect 3GS models when using iOS 4. This will be fixed with a software update.
6. We have had some problems with the Auto White Balance in pictures on the iPhone 4. The problem, as far as I can tell and have read is fairly limited to very specific lighting conditions - usually involving compact flourescent lights. This can cause pictures to look yellow. I have experienced this problem but only in 1 situation of my probably 30 or 40 places I have taken pictures. AWB is a software function, and I believe this will be improved if not fixed. AWB is tricky for every camera made - not just the iPhone 4. Photographers know this is not an unusual problem with point and shoot type cameras with AWB.
7. The iOS iMovie app has a bug that would crash when exporting movies. It has been fixed with an update yesterday.
There, that is my complete list of everything that I have either experienced or that I know is happening.
I am happy with our two iPhone 4s and AT&T. And I have lots of experience with Apple fixing or improving things with subsequent releases. Every single hardware problem Apple has ever had they have either fixed or mitigated with software patches, or they have had replacement or refund programs (some times even long after warranty coverage has expired). All of the people I have dealt with at AT&T have been very nice, professional, and helpful. And my network coverage has been good and I have had no problems with network aside from the previously mentioned 3G HSUPA problems (we are in one of the affected markets).
I recommend the phone, and believe that even the minor bumps will be worked out. As with any brand new product with brand new software there will be issues. If you are worried, wait a few months for the kinks to be ironed out, then pick one up. They will still be available then.