How difficult is it ?
I've read about people on here that wished they never did because of the errors etc they received. It's not quite a click of a button?
Very simple -- go to the iPhoneZA forums for help, lots of people have already JB'd today -- you will also find all the stuff you need to get going -- actual JB takes only a few minutes.
Btw with any custom modification there is an element of risk; there-in lies much of the Android intrigue. If you stay with tried and tested mods you won't experience much issues, also if you use only the Cydia App store to apply the changes then it by default takes a backup of the state before the change I.e. very simple to uninstall any mod if it gives you problems.
There are a ton of mods -- it's pretty much going to be like being a kid in a Candy mod store...
For example: would you like to scroll the pinned icons at the bottom of the screen, simple apply a mod, would you like to have a moving background like Android, simple apply a mod, would you like to have a lock screen like Android, simple apply a mod, .... And so it goes...
You will also find that some products / mods are for sale in the Cydia store, for example: 3G unrestrictor
Don't worry you can save those dimes by adding sources (mod servers) that have a "free" version
And remember if all else fails, you can always restore your last backup before the JB
http://iphoneza.co.za/forums/showthread.php?tid=1937&pid=23188#pid23188
Oh and btw only the Mac version of the JB has so far been released; the Windows version is expected next week -- if you don't want to wait and don't have a Mac -- I gladly help, let me know.