Amidst all the conflicting reports about Vista Service Pack 1 (some say it'll arrive soon, some say 18 months from now), the fact of the matter is that some people have a beta of SP1 already, and that means it's now been leaked to the rest of the world. APC acquired and installed that beta, and posted some opinions on it here. Here's what you need to know.

• Performance is "very noticeably" improved, with "far less hard drive thrashing" and better responsiveness.
• There's only one new feature included in SP1: A "Create a Recovery Disc" system that lets you build your own recovery DVD which lets you create a new install disc without a Vista install disc. Sounds useful.
• There are over 130 updates included (rumor confirmed), but little information on how exactly these updates work or what they do. APC includes a long list of components that have been updated, but no news on what exactly has been fixed in them. It's not their fault: Since Microsoft hasn't released the beta officially, APC has no way of knowing. That said, various changes (likely just stability bug fixes for the most part) have been made to a wide variety of services, including the backup system, indexer, MovieMaker, IIS web server, remote assistance, tablet PC system, and storage management. Look at the list about halfway down the linked post: Virtually no part of Vista appears to have gone untouched.
• The two fixes released last week are also included.
  

As for their opinion, APC doesn't speak much about its hands-on experience except to say that those performance improvements are worth the price of the upgrade alone. Frankly, that's good enough for me. 

LINK: LEAKED: Vista SP1 analysed in-depth