I used an iPhone 4s for about 6 months to get to know it better as I do sell a lot of iphones and need to be able to answer software related questions faster......
for ME I was VERY happy to switch to an Android, the lack of customization was a big thing for me, as well as the camera (wasn't impressed), lack of voice nav (now fixed), no swype (although tbh I never searched for a 3rd party app), the integration with some of my tools (software) wasn't there, I HATE iTunes, graphically it was only so-so, flash issues, lack of expandability, proprietary cable (yes it makes me mad that they can't use a Micro USB cable like everyone else) no HDMI output (without adapters), no menu button (I use the death out of that thing), no USB options (need mac adapters), google voice integration is almost non-existent, screen size is another biggie.... I LIKE large screens! sue me if you want!, and finally the clincher is probably that as a retailer/cellular company Apple is a PITA to deal with, no profit margins, pita for warranties (as a 3rd party carrier), and the fact that until just recently you had to HACK the phone to be able to use it on another network (we now can do factory unlocks starting at $30).
So those are MY personal issues with the iPhone.......
Now when customers ask about them, I tell them they are a VERY solid phone, easy to fix, tons of accessories and overall solid devices.