Not a techie, but as I understand it, group Hangouts aren't compatible with XMPP. Pidgin works solely for one-on-one chats.
I actually like Hangouts in theory (GVoice/Skype/GChat in one!), but it's a bloated monster of an extension that absolutely should not run in-browser. Even on my relatively powerful computer, I disabled Hangouts in Gmail just to function. I don't understand why Google can't build something as lightweight and beautiful as Pidgin.
All other critiques aside, it's telling that any users are coming to this conclusion because for me, a huge part of moving to GTalk/Hangouts back in 2006 or so was that I didn't need to install another IM app. I typically kept/keep Gmail open in a tab whenever I'm at my computer and it was great to not worry about Trillian or ICQ or AIM or any of those. When I was working at low-level jobs right out of college it wasn't always permitted or feasible to install applications like that on shared computers anyway. In-browser chat was a godsend and I liked how I could add my AIM account back when that seemed to be one of the more popular IM options among my non-techie friends.
Honestly I think Gmail/GTalk owe a lot to AOL for allowing that interoperability. Sites like Facebook would never allow you to connect with Google+ and use a competitor's site to access their platform. It takes away their biggest advantages (critical mass and inertia).
But it's right after lunch and I'm getting off topic. Personally I still use Hangouts as my primary IM/chat platform because it doesn't seem to give my systems much of a performance hit and it lets me carry conversations between machines and my phone without having to install apps all over. I use Pidgin at work but for everything else, Hangouts is still my default. Doesn't mean I'd mind performance improvements though.
Only works if have got a Gmail account. I had been using Gtalk with a Google account custom domain and that's gone. Took me a lot of time to realize my SVR records were not the problem. I created a new account with Gmail and everything works fine.
Is it an old account from before Google Hangouts? Mine was a new one after that. I think I really understood what should be done but perhaps I missed a step. In any case, creating a Gmail account "fixed" it.
I do most of my development on Ubuntu but I still have all my productivity apps on Windows, and on that platform Hangouts' interface is just horrible. I keep hoping they will release something better, but the desktop is not where their energy is being expended these days. At least if they used XMPP third-party devs for whom the desktop remains relevant could create better clients. As it is now you either live with Hangouts or move off the platform entirely. Sort of odd and depressing to have ended up here, imo.