Aloha everyone,
I think you're just confused on jailbreaking the iPhone as opposed to unlocking the iPhone. I've successfully jailbroken my iPhone after every firmware update, and a simple Restore from within iTunes removes all 3rd party apps and "restores" the iPhone back to factory specs for that particular firmware. You will have to wait for the iPhone to re-download all of the music, video, etc... that is normally synced from within iTunes, however, so that may take a few minutes.
While I can implicitly condone jailbreaking the iPhone, I do NOT, in any way shape or form, condone unlocking the iPhone. The reason is simple - Apple has partnered with AT&T to produce the iPhone, so it is within their purview to brick your iPhone if you deign to use it with another carrier. After all, in the US, you can ONLY use it with AT&T or T-Mobile, as they are the only two GPRS cell phone companies in the states - the others use CDMA, which is incompatible. In other words, even if you unlocked your iPhone, you can NOT use it with Sprint, Nextel, Alltel, etc... It can ONLY work with AT&T or T-Mobile, period.
Furthermore, because Apple is making their money by partnering with AT&T, and you HAVE to modify the modem baseband firmware to unlock the iPhone, it is fairly simple for Apple to tell that the iPhone has been modified. As it is in their interest to prevent such, it should not be surprising that they would go to any lengths to prevent unlocking, even so far as bricking unlocked iPhones.
As for 3rd party applications, Apple has already come out and said that while they don't officially support jailbreaking the iPhone for 3rd party app installation, they basically don't care if the users install them, although future firmware updates may (read: probably will) break and/or wipe out the apps. That's the risk all of us hackers take - that the next update will render our hacks unusable or deleted.
In summary, as long as you're only installing 3rd party apps, go for it. You can very easily remove ALL traces of hacking by simply restoring the iPhone from within iTunes. I would NOT, however, do the downgrade from 1.1.1 to 1.0.2 then back up to 1.1.1 (the iNdependence method), as it is unduly complicated, thus introducing, IMHO, too many points of failure. If you go to
http://cashflowlogic.com/iPhoneJailBreak.html, you can download a simple app to jailbreak your iPhone and install 3rd party apps. As I mentioned before, you can simply Restore the iPhone to go back to 1.1.1 goodness, if you so desire.
HawaiiMacAddict