I bought, a couple of months ago, the new apple product and since then I didnt want to "jailbreak" it.
Jailbreak allows you to install third-part applications directly to your iphone using WiFi or Edge.
So I decided to try it out since Apple released a SDK for the iPhone and to be honest it rocks :)

The only thing really boring is that you cant do it from a Debian or any other Linux distributions apparently. So I had to use an OSX to do it with the ziphone application.

It took less than three minutes to complete the installation and I was able to install a lot of third-part applications like a NES emulator, Perl or gnuchess.

You should install some packages just after the Installer like the BSD and the Boss Tools.
By default, you have only 300mb to install applications and the Boss tools will allow you to exceed that limitation and use all the hard disk.
Once Boss tools installed just "tap" on free disk space and then "tap" again on "relocate applications". Dont use the other ones except if you know exactly what you are doing.

I installed also a couple of applications :
* sendpics -- send pics you took with your iphone by mail
* ideleteMail -- select all mails and delete them in one time)
* openssh
* services -- manage services like ssh, edge, bluetooth
* igo
* gnuchess
* mobilecast -- download podcast without iTunes
* imflow -- cover flow for you pictures albums
* and a lot more ...