Mega
I know I'm very late to the party, and Lion is only just around the corner, but I finally got myself a pet Snow Leopard this week.
I've been running Tiger since I got my current iMac and it always suited me, but several things have changed lately that pretty much forced me into an upgrade. The most pressing was the changes to the MobileMe calendar service, that would no longer sync with iCal in OSX 10.4 after May 5th. We use iCal and MobileMe calendar to manage bookings for our B&B whether we're home or away so keeping it running was essential.
My (belated) first impressions are very pleasing, especially with the circa 13GB of hard drive space Snow Leopard frees up compared with Tiger. I'm also loving the way Mail can recognise dates and addresses and allows me to send them straight to iCal or Address Book (similar to the way iOS does). It has made our bookings process suddenly 2 or 3 clicks simpler, especially now I can immediately click back to the email that led to the booking in the calendar.
I got a great deal on eBay for the Mac Box Set with family licence, so I'm also going to have to find time to play with iWork and iLife ... I use iPhoto and iMovie quite a lot so I'm looking forward to seeing what developments there have been in the last 4-5 years. I am also seriously pondering ditching NeoOffice (a Mac-only offshoot of OpenOffice) for iWork having seen Numbers doing some very pretty things with my profit/loss spreadsheet.
Overall, I'm as happy as a pig in muck right now, which is bad news for my productivity levels ...