With an estimated 80% of SQL Server installs still on 2000 over the next 6-12 months there will be large numbers of upgrades if for nothing more, 2000 and the hardware 2000 is running on reaching end of life.
The question will be when doing these upgrades, do they go 2005 or 2008. Features will come into it for some of the upgrades but not most. The real trick for Microsoft is to get as many major application vendors certifying their products for 2008 as quickly as possible, so when the upgrades start most of the core apps are dealt with. And also they would be wise to get Seervice Pack 1 out early, as so many sites wait for that as a physiological barrier.