I had a jailbreak on my original iPhone when there was no App store, but since then I've never really had a compelling reason to jailbreak (particularly a tethered one). When the untethered came out for 4.3.1, I gave it a go again and wasn't at all impressed.
IMO, Cydia is a mess there are far too many adverts scattered around: It looks more like a site hocking dodgy diet pills or a "cure" for male impotence than a serious tool. On top of that, some of the prices for the smallest of tweaks are ridiculous.
The jailbreak lasted about an hour before I decided to go back to stock and I feel much happier with my phone in it's natural state. I'd actually switch the OPs question back round and ask what compelling reason there is for jailbreaking: I have unlimited texts on my iPhone plan, I already have tethering and have no desire to tweak the UI into something that looks like an Android phone (If I wanted a phone that looked like Android, I'd buy an Android

)