A few readers have asked, "Why is the NTC taking so long to capture Bani Walid and Sirte?"
Great question, and (luckily) simple answer.
Sun Tzu mentioned that you always want to give an enemy the ability to retreat. If not, they'll fight to the last man, taking many of you with them.
In past battles, Gaddafi forces have had the ability to retreat, and chose it, rather than be overwhelmed and destroyed, in the hopes of being able to reorganize and counter-attack.
All of Gaddafi's remaining forces are in these two cities, and they have nowhere to retreat to. They will need to be completely destroyed (surrendering counts) in order for the NTC to take these cities, which will be expensive and painful.
But ultimately, it is inevitable. The Gaddafi forces in Sirte have no supply lines and will fall to a siege. But, knowing this, they are likely to try to launch a counter-attack against NTC forces rather than be starved out. It's unclear whether NTC forces have significant reserves to deal with a counter-attack. Some rumors fly that they're stretched thin and are low on ammunition, but it's a game they're going to win in the long-term.
The problem is that people hate waiting.