There are so many more things that are likely to void your warranty than modifying the software. Inside the phones in several locations are little stickers that turn color if they get wet. They also turn color over time sometimes. Any impact damage regardless of functionality. Got a little scratch on your glass? well you dropped it and thats why it doesnt work.
If you've owned your Desire for 48 hours and everything works it's likely to continue working, although I bought mine outright and kinda choked a little when I did the upgrade knowing I know longer had any protection. The YAFFS2 file system Android uses is very efficient when you consider how NAND memory acts. Now I'm not sure what HTC's track record is for quality control but I did try and find threads about broken HTC's and such before I bought mine. I couldn't find much.
MOE3754 - I was talking about you when I said it was mentioned in this thread! After reading this I looked at the other thread and then a few more and took the plunge. I also DID HAVE SOMETHING GO WRONG with one of the 3 I flashed. I was able to recover easily with a battery removal.
When I was an early adopter of the original USA-only iPhone 2g (don't flame!) I had to constantly hack it to do any updates, or get any apps. I must have bricked about 3 of them (all could be recovered - one I had to wait a week for till someone came out with a new tool). It's only software and can usually (almost always?) be fixed if you just google it or ask for help.
Don't let fear stop you from doing this upgrade, you DONT NEED TO ROOT, its really like 3 steps and it does make a huge improvement. I really wish I did it earlier except theres alot of different routes and methods and I didnt really like any until I saw this one.
The Telus push is coming eventually, why bother? - Well when you do it you get a clean, unbranded (no extra apps you cant remove) 2.2. Apparently you also get future updates when HTC makes them available over the air, and you dont have to wait for Telus anymore (if you keep the gold card in). You also get the satisfaction of not having to rely on a company that doesn't seem to care too much about getting you the updates you want. You'll notice an immediate improvement.
Thanks again MOE3754!
Zak