New guidebook due out in October.
Private B&Bs in Bukhara, Samarkand and Khiva accept dollars or som, but if you pay in som they convert at the black market rate, so it makes no difference whether you pay in dollars or som (provided you do your money changing on the black market).
On the other hand, state hotels in the above mentioned cities, and ALL hotels in Tashkent (the exception being backpacker joints like Gulnara and Mirzo) usually quote prices in either dollars or som, but accept only som even if they quote prices in dollars. If they do quote in dollars (say $40), you'll pay the som equivalent converted at the official rate (1550S to the dollar), thus 62,000 som or so.
This is GREAT for the traveller, as you can buy 62,000 som for about $30 on the black market. So the REAL price of the room is only $30 (unless you make the mistake of buying som at the official rate or paying by credit card!).
That is ominous news about hotels requesting reg slips. It may be that the gov't will begin pressuring hotels to deny rooms to people who lack reg slips. But the reality is that officially you do NOT need a reg slip for every night you stay in Uzbekistan. Technically you only need a reg slip if you are in a given town for 3 or more nights. But hotels may not realize that. It will be interesting to see how this evolves.