Did mine skiing a month ago, surgery next Tuesday. Specialist has said wk 3 after surgery wind trainer, wk 4 gym, wk 8 xc bike and maybe wk 16 skiing (not fazed if no skiing this year). Full recovery I believe does take 12-18 months. I have been pushing myself hard with training to get my leg as strong as possible before the opp, lots of XC, gym etc. Muscle just falls off without the ACL, blew me away how quickly. Going for the last DH ride this Sat for a few months.
And Red Peekay, skiing hard (I guess we all have a different idea of what hard is) definately requires two ACL's, skiing at moderate speeds in control does not, as I discovered for the last 10 days of my trip...
Edit - I should add you can still ride without an ACL, no nerves in the ACL so it's not painful, I actually find riding XC makes it feel better and DH I just back off a little.