The list would take too long. Let's start with iPhone 4s. Looses wifi constantly. Like five second intervals. As a result can't take advantage of updating without hard link. Crashing of apps. Constantly. Several won't even load. These apps all ran before iOS came out on my iPad 1 and iPod touches, which the iPod touches run much better than either of the two newer supposedly more advanced devices. iPad 2 won't even download from app store. Ipad2 since last since now all photos are severely reduced in quality, way too pixelated to recognize people as anything but blobs. iTunes won't recognize iPad 2 or iPhone 4s about 50% of time, and now iPad is forcing a restore just to sync. Blah blah blah, it just goes on and on. Oh, and something new since iOS 5 too, half the time when you sync, a huge percentage of say podcasts, while they show up in device iTunes, are greyed out and you can't play them. Infuriating since that is what iPod is for.
I have noticed since reading the boards that the vast majority of people who don't have issues, have macs. Wonder if it's an ios5/windows issue.