I installed Snow Leopard on my MacBook Pro two nights ago. In fact, I left it installing and went to bed. The next day, I finished off the installation and left the machine running on my desk for a few hours. Later, I tried to grab a document from it over the network, but couldn't connect to it. Figuring it might just need a reboot, I went to shut it down. After a minute, I got a screen that you really don't want to see: the grey shutdown colour, with a darker grey circle and bar through it in the middle. Not comforting. I forced the power off, and went to reboot: same screen. Ugly stuff.
Presumably the recent Snow Leopard installation was a coincidence, and I just had a dead disk. Browsing to the Time Capsule from a different machine showed that the most recent backup was mid-morning, so there would be zero data loss. It turns out I didn't skimp, and paid for the extended AppleCare Protection Plan at purchase time, so the machine still has over a year of warranty remaining. All that remained was avoiding the multi-week diagnosis–waiting for parts–repair timeline that usually ensues. Next Byte offer a priority "tools down" service, where (for $A 175) your machine goes to the front of the queue. I figured since the parts and labour would be covered by Apple that I would fork out for it. I did, and I had my laptop back within 24 hours. It's currently restoring from the last Time Machine backup, which (even though I've jacked it into a spare Ethernet port) I presume will take overnight.