What kind of tweaks? I feel like this is some sort of secret society.
Sent from my Verizon Black 64GB iPad 2 w IOS 5.0.1 Update From NYC iPF.net
Things like CallBar (use your phone from the status bar - without interrupting anything), SBSettings (quick access to some Settings actions such as Bluetooth, WiFi, etc), biteSMS (SMS/MMS messaging on steroids!), DeleteAll (one-click clean of e-mail Trash), Activator (do everything with gestures; never use your home button again), iKeywi (have a programmable 5th row on keyboard), Overboard (see all your pages at a glance - go to them on the second glance), Move2Unlock (gesture-based phone unlock), PhotoAlbums+ (actually MOVE photos to another album in the Photo app, not just link them), Springtomize2 (many reasons) and Zephyr (an iPhone with iPad-like multigestures).
There's a whole bunch of tweaks, these are just the ones I have and find useful. I won't even get into the theming aspect of it. Have a browse through [the whole] Jailbreaking section of this forum and you'll see a whole bunch of folk are enjoying a whole bunch of "stuff" with jail breaking.
And, to bring this back on topic, I have all that I mentioned above, plus others, plus some themes and my iPhone is running fine; it's not bogging down, not crashing, i get great signal, apps don't crash and, as far as I can tell, there's no battery issues.
Again, zero issues with the jail breaking, whether it was with the tool TO jail break or running of a jail broken phone. If a person sticks with the more tried and true tweaks from Cydia and stays away from the dodgy stuff - the phone is fine. Of course and as always, YMMV.
Marilyn