I switched to the Desire about a week ago, it's fantastic! I was amazed at some of the stuff the N900 can do, but some of the apps you can get from the Desire amaze me more.

The social aspect of the Desire is brilliant. I can view any of my friends Facebook photo albums from the bog standard photo application. Same as their statuses, I can view any one of my friends status stream just from the contacts app. Then if I want to see everyone's statuses, it's available from HTC's Peep, which goes on your desktop too. All this applies to Twitter too. Of course, there is dedicated apps to view statuses and what not too.

Google Voice Navigation is spot on too as it works in the UK now. Tie this in with street view, and it's simply brilliant for finding your way.

Out of the box (no rooting etc.), I'd probably say if you are a heavy Social Network user, use navigation a lot, and like dedicated apps, than the actual website, then the Desire is for you.

If you like all the geek stuff (terminal etc) then keep the N900. There is a terminal app, and SSH app for the Desire, but I've not tried it as I never used them.

As for the speakers, they are poor, the N900's are far better!

Both brilliant devices, go for the one that enhances your productivity.

BTW, I sold my N900 on eBay for £295 free postage, immaculate condition, so you'll be lucky if you'll get that.