It seems to be the spiritual successor to Meebo webchat. So far its the only web-chat site that I have found that supports Jabber. I would absolutely recommend it!
imo.im is pretty great. I think they even had (web based) video calls with Skype accounts, at least until Skype restricted that type of access to 3rd parties.
Though it's not web based like imo.im, you also don't have to give your access credentials to a third party.