Sort of.
You need to download the IPSW file. Go to your device page, hold shift (on a Windows machine, I think it's Cmd on an OSX machine) and click Restore. This will allow you to select a IPSW to write to your phone.
Beware that this will erase everything off your phone and you will have to restore to a backup. This takes awhile too if you have a lot of apps. I'll probably do this with 4.3.5 to facilitate an easier upgrade to 5. Jailbreaking my phone is pretty useless now that AT&T is cracking down on the evil tethering.
EDIT:
I'm considering removing the jailbreak from my iPad 2 as well. I like having XBMC, but given how rarely I use it... I may just try and work out a transcoding DLNA setup on my server.