I used to jailbreak during iOS 4-5 days. Spent a lot of time installing this or that tweak, feeling like such a cool "power user." Oh my, animated wallpaper and SSV Normandy replacing the words "AT&T" on the upper left corner of my screen. This or that tweak that let me access this or that feature with one less gesture than before.
What a freaking waste of time. And at what cost? Random applications written by anonymous people on the net running as root on your iPhone, with full access to your private data if they wanted it? You are putting yourself at extremely high risk by circumventing the iPhone's security and running all this closed source software as root.
Jailbreaking is a security nightmare, and you're not worthy of the term "power user" if you allow someone called chpwn or BigBoss to run closed source shit as root on your personal communication device. By the way, that jerk BigBoss wouldn't let me run his software if I blocked ads on my hosts file. WTF dude, let us live a little?
If you really want flexibility, at least go to Android, where they publish their source.
It finally took cold turkey---bought an iPhone 5 when it came out, with no jailbreak for months---to learn that I really like my iPhone the way God intended it: nice and stable and closed---and even if not 100% secure, still better than giving some random dude called p0sixninja full access to my device. I get more stuff done now---you know, real work that I need to get done for my real career and not messing with a half-assed implementation of Expose that causes my phone to reboot half the time (yeah---the instability and the random reboots are yet another downside of jailbreaking).