Thanks for the comments. I can appreciate a fresh install would be cleaner, but in reality most people who aren't buying a new computer will want to upgrade from Vista or XP when the release version comes out, rather than clean install, so Microsoft better have it sorted by then. I presume that's a large part of the continuing validation of the RC, and hopefully the error reports will make some small contribution.
The main reason I went for an upgrade is that my whole family uses the laptop (as well as a couple of desktops), and I get serious grief if MSN, Facebook etc aren't working properly, so I hoped to make it as seamless as possible and faster into the bargain. Which I reckon is probably quite a typical scenario.
Everyone was happy that it worked the same, but I immediately had complaints that it was taking longer to load; and just when I tweaked the power options to mostly Sleep rather than Hibernate, it went pear-shaped.