But if Ucraine is not paying and tapping off, it seems to me that Russia has no choice but to shut down. The pipeline AFAIK runs THROUGH Ucraine, so the Russians must shut off at home base. That leaves Europe in the cold.
According to "Gasprom" (russian gas vendor), Ukraine didnt payed for 2008 gas (not fully) and dont want to pay "europe" price in 2009. As result "Gasprom" stop deliver gas for Ukraine but leave Europe transit going. Ukraine start to steal gas from transit pipe ("Gasprom" say he have data from independent auditors), "Gasprom" decrease transit for amount Ukraine took and said Ukraine must return to Europe all they stealed. Then Ukraine shut transit pipe on their side and take all transit gas to themself. "Gasprom" stop transit as it dont reach Europe anyway.
This is official story as I know. Of course, I cannt say is it true or not.