Yes, spotlight will find Apple Mail files, because the version of Mail
shipping it Tiger has reverted to saving all mails as individual files in
stead of in mailboxes.
Will entourage go this route? I very much doubt it! Will MS make use of the
much vaunted APIs that as supposed to become available at some time? If it's
practical to do so, I would expect they will. The MacBU have never been
afraid to latch on to Apple technology where it will help improve their
product without causing undue problems elsewhere.
It all depends on what is in the APIs if/when they are published.
If you want an exciting (ish) look at exactly how Spotlight works with Mail,
iCal and Addressbook (the latter two of which use big monolithic databases),
try
http://arstechnica.com/reviews/os/macosx-10.4.ars/9
John Siracusa's stuff is always fantastic - pity he writes so infrequently!
If you can't make it through that, basically Apple uses the monolithic
databases as before, but for each entry in the database creates a completely
new proxy file for Spotlight's benefit. So for Spotlight to work with
Entourage, realise that at the moment, every calendar entry, address book
contact, task, note, project and email message would have to have a proxy
Finder file hidden away somewhere. Possible, but there are seriously better
ways of doing things and the amount of work facing the MacBU would beŠ
impressive.