But why do you buy a phone that you need to jailbreak when Android phones can be customized without the need to jailbreak? What is so compelling about the iPhone? Is it as simple as being rebellious? (I'm going to do it because Apple says I can't)
Disclaimer: I own an iPhone 4 and really enjoy using it, but am curious about the reasons for going that JB route.
Good question.
I like the iphone and iOS experience. Im not interested in Android or other mobile operating systems.
I just like to enhance it with some additions of things not available currently from Apple or the Appstore but only from Cydia.
Things like Bitesms, fakeclockup,Sbsettings,MyWi,activator,3Gunrestrictor,igotya and other availabe usefull packages for JB devices.
Im Not the I want to be rebellious type, Im too old for that

Like my bud Eastercat said above its not for everyone, most people should not bother and stay away from JB if they dont put in the time and effort to understanding how, what, why and many other things that jailbreaking does and each package they install to their device.
Im into computer programming all my life so I like to go deeper and further than the average user. Im interested in understanding and enjoy tinkering and fixing things that might go wrong with addons that cause issues with others and various conflicts that you might encounter.
Some users just hit the one button JB program for example. Then open up cydia and start installing every package there is out there or that sounds cool. Then they have probs and cant find why or what is the prob out of the 87 packages installed or the tons of themes, live wallpapers etc...
Then they're like ******* JB, this sucks

For me I like to keep it simple. I only download and install the packages that I need and use on the regural. Packages that are well known and by respected companies or authors in the JB scene. And I can count less than 10 JB hacks that I use and install. I have a very solid and stable 4S without any slowdowns, crashes or other issues.