In case anyone's interested in the process, here's my revision experience so far:
REVISION #1 (December '07-February '08):
Work required: Major structural and plot changes, changed main characters from adults to mid-teens
Length: Reduced from 104K to 94K
Total time to completion: Nine weeks (working 2-3 hours a day)
REVISION #2 (April '08):
Work required: Streamline and clarify plot, full line edit to fix pacing and clarity issues
Length: Reduced from 94K to 74K
Total time to completion: Three weeks (working 2-3 hours a day)
REVISION #3 (May '08):
Work required: Several additions and clarifications, minor line edits
Length: Only slightly reduced to 73K
Total time to completion: Four days (working 3-4 hours a day)
Coming up next should be copyedits, where a new editor looks at the ms. and marks it up for punctuation and grammar, while also noting continuity and fact-checking issues. And once that's done, oh glory, they'll send me galleys and I'll get to see how my story will look in actual typeset, book-quality print!
And also: *wrings hands* OUCH.