Some time back, I wrote a post comparing the advantages of Google Apps Premier over Gmail - you get more storage space, can undelete (or recover) deleted emails and ensure that there no false positives [the mail from a trusted source won’t be marked as Spam].
Robert Cringely at PBS offers a similar thought - Google Apps Premier Edition is pretty compelling. Remember Premier Edition will allow me to use my own domain, not just one of Google’s. The storage limit is currently 25 gigabytes per address “and growing,” according to Google, and a look at my server shows that by keeping every message since 1992 (remember that when you sue me) I have so far used only about 20 gigs, so 25 would do for now. Throw in Postini mail security tools and I am convinced, which was exactly Google’s plan. Link.
Both Google Apps and Gmail users will also have IMAP features very soon.