I am aware that o2 tv series ,and generally streaming 3gp files , is not the perfect solution. But this is just in case you have no other options for watching new episodes of your favourite shows :P

I, personaly, watch TV shows on XBMC on my laptop, but sometimes I like to use my N900 just because I love my phone

And N900 has enough power to run mp4 files. Not ALL of course, but the ones from o2tvseries.com it can, and the quality is not so bad