Personally, as many others have said before me in this thread, I came to the iPhone from a Windows Mobile, Palm and Blackberry background. I installed hacked ROMs on my Treo 750, AT&T Treo 750, 8125 and 8925 WM phones, installed beta OS's on my Curve and Bold, and even messed around a little with my Treo 650 a while back. That doesn't include the Pocket PC PDA's that I played around with, too.
All in all, all of the devices were eventually reformatted or restored to original, stock ROMs or OS's because of the numerous issues the devices had while "hacked."
My WM devices crashed on a regular basis, or locked up, and my Blackberries had memory leaks the size of the hole in the Titanic. They just never functioned as the manufacturer intended them to.
Now, I am no Apple fanboy, by any means, but the phone, as mentioned before also, just works. I have not found anything that I need it to do that it can't do (other than Flash, but that in itself is a huge security hole), either right from the box or with an app. Sure the device isn't open to installing any app we want, from any hack..oops..developer we find on the net, but how many untrusted apps did WM users install over the lifetime of their devices and got hosed because of it.
As people that have jailbroken their phones find it useful, good for all of you, but trying to convince me that it is good for me is useless. I can't imagine how many people go to Apple stores on a daily basis and try to return jailbroken phones to Apple because they are having problems with them.
I read a post the other day where the OP stated that he couldn't wait to get himself and his girlfriend a pair of new 3GS phones and jailbreak them right out of the box, like it was going to change his and her lives somehow.
But like I said, good luck to all of you that have jailbroken and love it. I will not be doing it, and see no reason why I should in the present or the future.