I did it in October 2008, coming from China. No problem, good weather (beginning of October). But 3 weeks later, it was apparently snowed-in.
Accomodation in Pakistan is dead-easy. Lots of guesthouses everywhere, including Sost.
Between Sost and Tashkorgan, I didn't see any accomodation, but plenty of spots for camping in Pakistan (get a good sleeping bag though
. And with good spots I mean: places where the bike/tent will be out of sight.
About 50km after Sost (going towards China), there's 2 checkpoints for the Khunjerab National Park. I'm sure they'll be more than happy for you to stay with them. I found Pakistan to be extremely friendly & accomodating. A guest is considered a "gift of allah" as in most muslim countries. Personally, I'd stay away from border-areas with Afghanistan though. But the Pakistani police won't let you go into dodgy areas anyway as they're usually concerned about your safety.
From Khunjerab Pass it's about 3-4h to Tashkorgan (China) I'd say. The KKH in China is a real blast - one of the best roads I've ever seen, smooth tarmac with not a single pothole. Accomodation in Tashkorgan is easy.
Tashkorgan to Kashgar: 1 day of riding, maybe 5-6h. Accomodation in Kashgar: Quiny Bagh Hotel (the old British Embassy), a well-known meeting-point for overland travellers.
Stans: Try to get as many visas as possible before you leave! Kyrgyzstan is the easiest, Tajikistan was easy too but it may change. Uzbekistan = usually OK , Turkmenistan Transit visa: pain in the neck. (Turkmenistan Embassies in Germany and UK are a nightmare, the one in Vienna is very friendly but 'temperamental'.)
Turkmenistyan Visa in Tashkent (Uzbekistan): can take a while (1 week maybe) but should be OK from what I heard from other travellers. Remember: for a Turkmenistan Transit visa you first need a visa for Uzbekistan AND Iran before you can apply for the Transit visa. (Bummer... it's always been my dream to become an illegal immigrant in Turkmenistan