Should also add, I bought a Panny BD35 for £215 lsat week (Amazon) and although the only Blu Ray discs I've got are the free one that came with the player and Kung Fu Panda which someone gave me, I have to say I think its worth it.
On the free disc (National Treasure 2 - Book of Secrets), some scenes look like DVD, others are noticibly sharper. Some of the trailers though look amazingly sharp - Pirates of the Caribbean (unsure which one), Chronicles of Narnia (Prince Caspian) are two of the trailers I remember looking amazingly sharp.
After watching National Treasure, I wasn't totally convinced as were only some scenes improved so I put on House of Flying Daggers DVD (everyone knows this to have possibly the best picture quality of any DVD out there). I've also upscaled this before on a Denon 1940 and been blown away. I have to say, after watching National Treasure, I was amazed how average H of F D looked. Even unsharp in places.
So in conclusion I'd say, yes it is worth it. Sometimes it appears more subtle than you might expect (maybe its so hyped we're all just expecting something it can't deliver), sometimes you can notice better sharpness. However, if you watch Blu Ray back to back with DVD, then you'll really appreciate how much better it really is.
Personally I won' be buying more discs until I can get some bargains but in the meantime, I have to say yes it is worth it.