UPDATE (08/05/2010)Got the error back this morning, so ignore what I say below.
One of the great features of Smart-Phones is their ability to accept and download software updates wirelessly - and HTC puhed their 126.96.36.199 to UK T-Mobile HTC Desire owners last week.
While I couldn't find any specifics on the web about what this update did, I have noticed that the random Micro SD Memory Card failure error that I have occasionally encountered, has gone away.
What would happen is that I'd go to use the phone and it would have an error message, saying that it had been unable to back-up my files to the memory card. If I tried to use the camera that would also say that it couldn't access the card, and a quick look at the memory settings showed that the SD card wasn't showing as being in the phone.
The only way to fix this problem was to turn the phone on and off, which takes about a minute. I tried formatting the card, both in the phone and in a card-reader, but the error would reveal its ugly head a couple of days later. I contacted T-Mobile support, but they wanted me to take the phone to a shop to look at it (like you'd be able to SEE the error!), but I just don't have the time. I was just going to buy another card and see if that solved the problem.
I can happily say that since the 188.8.131.52 HTC Software Update for the Desire, I haven't had this problem at all - so well done HTC, the only thing bothering me about my excellent phone has now been solved!
ps If you're still waiting for the update, look out for a message in the status bar asking you to confirm that you want to do the update. The phone will be out of commission for a few minutes while it does it, a bit like when you have an automatic update on your pc.