I don't think there has ever been a way for Apple to see if your phone is jailbroken or not. If you didn't like the jailbreak all you would need to do is restore to the last firmware when you sync your phone.
There's little risk - if it doesn't work, you can just do a restore and bring it back to normal.
As far as Apple, no - they can't tell if your phone is jailbroken or not. Typically the only way to undo the jailbreak is when an update is available to let it update. Otherwise just don't update the phone until a verified jailbreak is available.
I've been jail breaking from day 1 of availability. (? - purplera1n) I first used T-Mobile so it was a must. Now Im on AT&T but I prefer prepaid so jail breaking is still necessary. Aside from that, I like Cycorder (video recording app) and Google Voice app from Cydia and not to mention i had mms abilities over a year ago because of jail breaking. That goes for video recording as well. This is all one the same phone. Never turned into a paper weight. And I jail broke 4 other phones. Never an issue. Dev Team does amazing, and in my experience very reliable work.