I have it.
A few stories running around that require you to upgrade an existing Tiger, or Leopard installation. The answer is You Can, But You Don't Have To. I wiped the drive and pretended I had a clean slate, and it worked beautifully.
SafariBlock does not work, and most of the current ad-blocking solutions don't unless you run Safari in 32Bit Mode which while works, is not ideal. Anything that needs an InputManager isn't going to work either, the only solution that has the least requirements is the CSS method (which is also not really ideal because I don't think you can manually add sites to block).
QuickTime X does NOT have any Preferences Panes what so ever, that means no easy way to play video full screen on another monitor BUT you can install QuickTime 7 and get your old functionality back if you bought a Pro License.
You can add Perian 1.1.4 and regain...^AHEM!^ alternatively sourced material support.
QuickTime X also does not have the option to Play immediately upon opening a file. Not a deal breaker, but would be awesome if that's brought back in again.
Rosetta is now an optional install, but what the hey, it's only like 3.5MB extra...
You can use Four Finger Swipes on older MacBooks. Nice, but really...eeehhh..yeah its ok I guess.
I saved tons of space. For example on my 10.5 install on my MacBook Air w/64GB SSD drive I had only 40GB remaining after the essentials had been installed (iTunes and iPhoto).
On 10.6, after installing the above as well as iWork, I have 49GB free. That there is enough of an excuse to upgrade.
I also highly recommend an external hard drive for your media (nice catchall for documents, photos, music, games etc). Not only does this mean less space is taken up on the internal drive, it also means if you have to take your computer down for upgrade/reinstall its less work getting everything back into place. And if you have MobileMe it means even less work as it copies all the Favourites, Address Book, Mail and Keychains back in for you.
Thanks for the info. I need to talk to my Mac-guru brother-in-law to see what we are going to do with the 10+ Macs we have between the two families and his business.
Should be an interesting time.