Yeah the OTR plugin is really nice. I think it has suffered from some serious not-invented-here syndrome in terms of not being baked into Pidgin as a core feature (which it should be).

It has been included in Mac OS X's Adium client for many years, which probably means that it has the largest installed base of any end-to-end encrypted chat client, other than Skype. (Although I don't know if Adium automatically enables it, but at least it doesn't require another download and a clunky plugin enablement.)