Their bar is quite expensive (although this is relative to other colleges - the prices are still very low in comparison to most pubs).
Don't ask anyone to comment on DSU, you'll probably just end up with a string of expletives. The only half-decent thing they put on is Hound (a clubby type thing) on a Friday night, and "I Can't Believe It's Not Cheese", an indie-rock-punk-emo type thing that is on about twice a term on a Wednesday. Despite having a huge venue on the ground floor (the Fonteyn Ballroom, capacity ~1000) they've never had any bands I've ever heard of playing there - except for Hell Is For Heroes, and they sold too many tickets for the (charity) gig, which had to be moved to Walkabout, which had a greater capacity, due to being an old cinema.
So yeah, DSU isn't exactly great, but there are loads of gigs in Newcastle, generally at Newcastle Uni, or Northumbria Uni. Occasionally there's a good band on at Sunderland Uni (which is where I saw the Arctic Monkeys) too. With the opening of the Carling Acadamy in Newcastle too, there should be an influx of new bands into the local scene.