I have the same problem, starting 4-6 weeks ago. I use kernel power47 and power48 on my other n900. But cant see my gmail contacts online anymore. Also, if i click on an gmail-contact now, it sends a request to chat to that contact every single time
I suppose Google wants to keep this functionality exclusively in Android or something?! Even then, it should be possible to update Maemo in order to make it work again! (thanks to everyone working on this)
But i am able to send IM messages to gmail-contacts though, and THEN i see if they're online or offline from my own message status.
Another way to work is to use the agent switcher for browser MicroB and open your gmail-account. Click on chat and there you see your online contacts. I dont know how often it refreshes