Lagginess, lack of free apps, no need for further customization. Mainly lag.
What apps do you have installed? I've got quite a few on my iPhone 4s and i don't have any lag. Anyway, before assuming it's the jailbreak that is slowing things down, have you done some troubleshooting? It's quite possible that it is an App that is causing issues of you just have a problem with your iOS install BECAUSE of the jailbreak. A reinstall, setup as a new device, and re-jailbreak would probably fix it.
Here is what I've got installed:
Activator - Free, but I could do without this, but it is part of DashboardX.
AdBlocker - Not free, but nice.
AdBlocker Networks - Free.
AntiTint - Free
BlurriedNCBackground - Free.
Browser Changer - Free.
DashboardX - Not free, but awesome.
f.lux - Free, and this right here is one of the main reasons why I jailbreak.
iCleaner - Free.
Jukebox - Not free, but a neat little tweak.
NCSettings - Free, and this is another one I jailbreak for.
Nitrous - Not free, but I like Chrome better than Safari and it speeds things up.
NoCoverflow - Free.
OmniStat - Free.
Springtomize 2 - Not free, but awesome.