certainly. I am indeed running 3.0 on 3gs although the issue also appears on 3.0.1 and 3.1 as far as I know. I am in UK and use Vodafone network but again, same issue appears on other networks when i travel abroad. and to add complexity to the whole thing, I have tested Devs and Geohot's jaiblreak with the very same results. in both cases issue exist and I didn't notice any difference apart from battery life which was much shorter after Geo's jailbreak and unlock. combination of Geo's jailbreak and Ultrasnow caused exactly the same effects: battery drainage and signal strength instability.
my question is: did anyone observe any similar signal problem? also, when you are on the move, let's say on the train and your phone is switching base stations, did you notice that if 3G is gone even for a while, phone shows complete lack of GSM signal and then shows availability of GPRS network. it's almost like: 3G, no signal, GPRS.
I am still trying to isolate the issue but if you have any ideas re: how to solve problem I would be very grateful for help. btw, this is rather not a phone issue as the other 3GS which I own suffers from the very same problem.