The rebels are poorly organized and don't have many heavy weapons, but they have plenty of fighting spirit and enough small arms to field, in most cities, a few hundred to a few thousand soldiers. Many have military grade weaponry, and they're supported by lots of civilians taking potshots with hunting rifles, shotguns, pistols, Molotov cocktails, etc. I haven't seen much evidence of the rebels effectively using the tanks and heavy machine guns that they apparently have captured. Their forces have no chain of command but they seem to be able to fight competently.
For example, yesterday the government forces attacked the city of Brega (a smallish place with a strategic port/oil facility and an airstrip about halfway between Tripoli and Benghazi). They quickly took the port, the oil facilities and a university, which as far as I can tell on Google Earth are all on the eastern side of the city a bit away from the more populated areas. From watching videos of the fighting, it seemed that the government forces attempted to press the assault into the denser areas of the city and were pushed back. At some point the rebels were then able to call in hundreds of reinforcements from the next town over, and actually had something like a coordinated assault on the government troops which recaptured the oil facilities and port, then cornered and destroyed some of the government forces on the university campus. My guess is that most of the government troops ran away and that only a platoon or two was actually surrounded and destroyed. To successfully counterattack, the rebels had to advance across open sand dunes under fire from enemy infantry who were on foot and mounted in pick up trucks and possibly other vehicles, as well as sporadic mortars/artillery and even a few ineffective air strikes from a single jet fighter.
To me the course of the battle shows a few things and one of them are good for the government.
First off, the rebels are learning. Videos of the battle show them to be amateurish, but by all accounts they managed to coordinate their actions at some level. They
took offensive action. They counterattacked after an initial defeat. These are not things that a mob can do. Most of them don't know it's a terrible idea to point an AK at an enemy hundreds of yards away and let it rip on full auto, but somehow they managed to make a successful infantry assault on a stronger enemy position. Don't underestimate the importance of that. In contests between less-than-professional forces like this one, psychological factors are often the most important thing.
Secondly, we know the rebels are brave. Unlike most irregular, semi-trained forces, they are willing to stand their ground against a superior enemy and take the offensive. They faced an enemy that had far superior firepower and a bit of surprise. They attacked across open ground into some pretty heavy firepower. And there was no one forcing them to do these things. Their morale seems to be very good and their confidence and experience is growing as they win battles. They won't go down without a serious fight now.
This brings me to my third point. The government forces seem to be pretty cowardly and incompetent. No truly professional force that knows how to use firepower should have been pushed out of a defensive position by a bunch of civilians with small arms advancing across open ground, no matter how brave the civilians were. Replace Qaddafi's security forces with professional troops from the US or the PLA and it would have been a massacre. The government troops had access to artillery and mortars and even air strikes. Yet they were defeated. Why did that happen. This is why: corrupt dictatorships generally have pretty bad officers and poorly motivated soldiers. Look at the Arab nations fighting Israel, Saddam's army, South Vietnam, the Guomindang, Tsarist Russia etc. etc. Corrupt and unpopular regimes rarely field effective fighting forces. Mercenaries and hired goons will desert or switch sides rather than fight if they think they're going to get killed. Fighting against your own people makes all these problems even worse. Contrast that with the rebels. They obviously will fight to the end because they are fighting for a cause, and they know they will probably all be massacred if they lose.
Here's some more combat videos.
^That video shows the rebels are still amateurs in many ways. There's about 10x as many guys standing around watching, throwing stuff, chanting and yelling, or talking on their cell phones as their are guys actually shooting at the enemy. I suppose that's what happens though when every young man in town wants to get his cred as being a "mujahideen for the revolution" but there aren't nearly enough guns to go around.