It is totally not like that at all. It's more like buying a porsch and after getting it home you find out the the Porsch company had installed artificial and arbitrary performance limits on nearly every aspect of the car. What JB does is remove some of those performance limits so you can have things like:
- multi tasking
- more icons in the dock
- more icons on the home page
- folder-like categories
- call blacklisting
- internet tethering
- a much more useful keyboard
- caller ID blocking
- lock screen items like email, weather, news, and SMS
And many other very useful features that should have been included in the stock phone but that Apple decided not to include. I've been running JB iphones and iPodsfor over a year and have yet to have a single problem.
I like that analogy. Well observed and true.
I also have a jailbreak on my (factory unlocked) 3GS. For most of the mentioned reasons. And most of them will be obsolete with 4.0
That's why I will take my time to make a decision if I want to jailbreak 4.0 again. For the moment I doubt it, but who knows, what cool features I want by then.