Pro-Qadhafi forces in Sirte have rejected the National Transitional Council ultimatum to surrender, meaning the NTC forces (:"rebels" seems a bit overtaken by events, given widespread international recognition) will presumably have to mount a full campaign. But two weeks ago, everyone expected Tripoli to require a long, hard, slogging battle against last-ditch defenders, but the city fell with surprising speed.
Certainly the exp4ected resistance in Tripoli evaporated quickly. The hollowness of support for the regime, despite brutal measures to hold the line, saw resistance crumble. Sirte may be a tougher nut to crack: Qadhafi's native town, with tribal allegiances to him, and a town that has benefited from government largesse (as a small town that has come to host African summits regularly), and with a lot on the line.
The question, I suspect, is whether the regime's dwindling support has reached a point of no return, where (as happened first with Russia in 1917 and then with Germany in 1918) the army simply melts away. Qadhafius African mercenaries have no incentives to fight tot he last man; but some of the regime's elite forces may still have fight in them.
Meanshile, the explosion of a car bomb in Tripoli is a reminder that, as was the case in Iraq, the capture of the capital does not assure an end to violence.