Offering a preview to testers already (and already leaked), Microsoft concurs with earlier statements in a more cement fashion about the release date. We can expect the service pack no sooner than 2008, which means it may come near or at the same time as SP3 for XP. Faced with adoption issues, Vista definitely has lots of room for improvement, and some of the needed improvements are coming.
In particular, SP1 for Vista will include the ability to encrypt both the OS and data partitions, and not just the data partition as it stands now. EFI support will be added in some fashion, along with a newer file system for removable storage. Probably to the chagrin of others, a Microsoft employee also stated that XP's service pack is an “end of life” roll-up for the OS.
The big question is whether or not Vista SP1 will make it a worthy upgrade to XP. In the eyes of many, Vista is still not worth it. Valve, for instance, sees no reason currently to develop for DX10 due to a low percentage of gamers using Vista.