Am due to upgrade in a weeks time and am stuck between these 2 phones.

Anyone here have experience of either of them that they'd like to share and help me decide?

I have a desire and I can't fault it, (apart from the battery life that is, but you get that on most smart phones) had a few samsung's in the past and they are a little clunky to say the least!

I was in the same situation, went for the galaxy in the end and glad I did. Have used a desire quite a bit as my mum has one and I did all the initial set up on it so know all the ins and outs. Galaxy has better screen, slightly better battery life and plays most video file formats out the box and also has swype which really is a joy to use! These all made the choice much easier for me. As for build quality its very nice. I do however miss some of the nice features which sense has like friend stream etc but I can live without these for all the other features. The screen on the galaxy really is amazing and a joy to look at.

I have the desire, my friend has the galaxy. The ONLY advantage over the desire is that it has a better screen, but that's not to say the desire has a bad screen because it's brilliant, but the galaxy's screen is better. I don't like the feel or the build of the galaxy either, it's very cheap feeling. Also it doesn't look very nice being an iphone rip-off. I do like the swype feature, and that is the only thing that I would want the phone for. However swype is working on a release for android phones, and often opens a beta download.
The desire is MUCH smoother also when moving between screens. The galaxy looks choppy compared to the desire, which is as smooth as the iphone.
Overall I'd say the desire is a lot more perfected. On paper the galaxy should have the edge, but having tested both, the desire is much more enjoyable to use and also easier. Also it has better home widgets.