In reply to tnj:
From personal experience and things I've read from time to time:
1) Don't spend too long in one place. I find that if time is limited, I make every day count, if I think "well I've got another month here" I am much more laid back, get up late, chill out, don't get nearly so many routes done. I'm thinking that about 2-3 weeks before moving to a new area is good to keep me motivated every day, I'm sure it varies for everyone else.
2) If 8a is your holy grail, I wouldn't take as long as a fortnight off climbing at a time, maybe a week if you feel really wrecked.
3) I would either train indoors or go somewhere like Malta/Sardinia/Sicilly to continue sport climbing over the winter rather than take time out skiing.
4) For a single pitch 8a, you really don't need multipitch fitness. The fitness you are looking for would almost certainly be better built up on long single pitch 7a/b/c routes.
5) You said you get injured bouldering and personally I don't really enjoy it but I'm pretty sure that if 8a is your target, it would be a lot easier to access if you had at least a couple of bouldering periods for pure strength in there somewhere.
Disclaimer: This advice isn't really based on any sort of training program or science!
I suppose it depends a bit on what type of person you are. If you are the kind who can get psyched about training, go down to the bouldering wall and spend 2 hours doing the same circuit with a weight vest on every night for 2 weeks and drink only protein shake, you should have no trouble getting to 8a if you get Robbie Phillips or Neil Gresham or Dave MacLeod or someone to recommend you a training program. If that sort of approach would bore you silly then you might be better off concentrating on getting the most enjoyment out of the year, climbing in lots of interesting places and (while still pushing yourself) making a grade aspiration take second priority.
Also, I e-mailed you.