I switched to iphone 4 after owning many NOKIAs. I have bought additional iphones, 3GSs that I have given away to family and children. The only complaint I got is battery life on 3GS. The battery life on iphone 4 is fantastic.

The reason I switched is simple. It works. Never had issues with email, never had issues with random reboots and the quality is just top notch. The search function is the best ever and VKB is by far the best. Google maps is perfect. Overall its a high quality phone that does what it advertises extremely well and covers all the basics without a hitch.
Nokia on the other hand made nice hardware. I loved my E71, except I couldnt search the phone, the function was waaay tooo slow, the email sucked big time, the fonts were wayyy tooo small and you needed to buy a separate program to enlarge them.

Its the difference that keeps getting bigger. Apple pays attention to the minutest of details. NOKIA pays attention to bottom line, and that bottom is getting harder to see for NOKIA. If I was a CEO of NOKIA, I would personally inspect the device in every continent and deliver a summary of all the defects I identified as a user, and have the team work day and night to fix it. Steve Jobs did that. It doesnt seem like anyone at NOKIA is doing it. Their quality control is gone down the tubes. Apple quality control is superior in many ways.