I dropped my phone a while back and the back got a small crack in it. Luckily I have accidental damage coverage, so I went into the store today and asked them for a repair quote for me to submit to my insurance company. However, I totally forgot to restore (unjailbreak) my phone before going in, so I got kinda nervous at that point. When I went up to the tech, I brought it to the serial number page myself so she wouldn't see that I had lockinfo, bitesms, etc installed.
The first cool part of the story is this: she looked at it, said "oh, all you need is a new back plate?" *looks up serial number* "Your warranty expired 20 days ago, but don't worry about it." She then printed out a repair authorization form that said "Back plate. Unit Cost: $29.95. Total Cost: $0.00." and told me to initial and sign it.
I wasn't about to argue the fact that dropping your phone isn't covered under warranty. She took it to the back and popped a new back plate on in less than 5 minutes. 
The interesting part is this: while she was in the back, I spoke to another tech and asked him point blank, "what is Apple's stance on jailbroken phones and warranty?" He replied that if it's clearly a hardware problem that isn't affected by the jailbreak, it's still covered. They'll first do a restore (presumably to the latest firmware...take note for all those who have an unlock on an older firmware!), then see if they can still replicate the problem. He also said that they run an "AB test", which seemed to be some sort of software diagnostic...he didn't explain further. Something like a broken home button will obviously manifest itself whether or not it's jailbroken, so that will be covered under warranty. Something like decreased battery life, however, could be a software problem that comes as a result of jailbreaking, and therefore it's not conclusively covered under warranty. (Both of those examples were his) I then asked him if the serial number of the phone gets flagged as being jailbroken in Apple's system, and he replied that it does, but again, that doesn't on its on void your warranty entirely. He then asked me why I jailbreak my phone, and I told him it was for the increased functionality. He agreed that it's nice, but that Apple usually ends up implementing a lot of things (like notifications) in official iOS releases anyway, so he'd rather just wait for that. He specifically said the words "I haven't jailbroken yet," implying that, as an Apple tech, he could jailbreak his phone...
Finally, the tech came back with my phone and turned it on. "Uh oh," I thought, "now she's going to see Lockinfo and my SN is going to be flagged". Sure enough, Lockinfo popped up, and instead of her giving me a weird look, she just smiled and said, "oh, you have this too? I love Lockinfo, I use it all the time." My eyes did this:
I said, "wait, you have your Apple-issued iPhone jailbroken???", and she replied, "yeah, I love it. We're not supposed to, but c'mon, look at how great this is!" We then talked for a few minutes about all the great things you can do with a jailbroken phone, like the infoshade in lockinfo and bitesms quickreply and all that. That's one conversation I thought I'd NEVER have with an Apple tech! 
The first cool part of the story is this: she looked at it, said "oh, all you need is a new back plate?" *looks up serial number* "Your warranty expired 20 days ago, but don't worry about it." She then printed out a repair authorization form that said "Back plate. Unit Cost: $29.95. Total Cost: $0.00." and told me to initial and sign it.
The interesting part is this: while she was in the back, I spoke to another tech and asked him point blank, "what is Apple's stance on jailbroken phones and warranty?" He replied that if it's clearly a hardware problem that isn't affected by the jailbreak, it's still covered. They'll first do a restore (presumably to the latest firmware...take note for all those who have an unlock on an older firmware!), then see if they can still replicate the problem. He also said that they run an "AB test", which seemed to be some sort of software diagnostic...he didn't explain further. Something like a broken home button will obviously manifest itself whether or not it's jailbroken, so that will be covered under warranty. Something like decreased battery life, however, could be a software problem that comes as a result of jailbreaking, and therefore it's not conclusively covered under warranty. (Both of those examples were his) I then asked him if the serial number of the phone gets flagged as being jailbroken in Apple's system, and he replied that it does, but again, that doesn't on its on void your warranty entirely. He then asked me why I jailbreak my phone, and I told him it was for the increased functionality. He agreed that it's nice, but that Apple usually ends up implementing a lot of things (like notifications) in official iOS releases anyway, so he'd rather just wait for that. He specifically said the words "I haven't jailbroken yet," implying that, as an Apple tech, he could jailbreak his phone...
Finally, the tech came back with my phone and turned it on. "Uh oh," I thought, "now she's going to see Lockinfo and my SN is going to be flagged". Sure enough, Lockinfo popped up, and instead of her giving me a weird look, she just smiled and said, "oh, you have this too? I love Lockinfo, I use it all the time." My eyes did this: