This is my rule of thumb. Only jailbreak if you have a overwhelming need, desire that is not satisfied by Apple.
One reason for that is it voids your warranty I believe. If you need service, you will have to restore to factory. I don't know if Apple has a way of monitoring what phoned are jail broken or not. When the latest updates come out from Apple and you want the features you have to wait until a jail break team figures out away around it.
In my case, my desire was to run Slingbox on 3g. If not for the app coming out wifi only, I was perfectly content with a stock device. I have not installed any crazy ass themes, I have no need to ssh into the device, I only install the bare minimum of what was needed to get Slingbox working.
Just my thoughts, others may tell you different.