I've been with them since about June 2007 on their 3 discs at once subscription. In that time I think I've averaged around 12 films a month, which means each rental is just over £1 for me, which I don't think you'll beat if you look anywhere else.
Yes they are sometimes slow with getting you the top priority titles, but they do eventually come. They are also really good with TV shows, I recently go sent all 6 discs to Studio 60 on the Sunset Strip in the space of a few weeks. Once I got the first disc, they then all followed.
Blu-Ray wise I probably get 3-4 a month and I'm sure as time goes on with Blu-Ray releases in the future, this number will grow. If you look about on the net I'm sure you can get like 3 months trial voucher if you're still not convinced. Overall I'd happily recommend lovefilm
p.s this week I was sent the wrong disc for the first time, apart from that small blip, all the discs I've rented in the last 8 months or so, I've never had one playback issue due to scratches