Just to make sure I'm adequately managing expectations: the military situation on the ground in Syria is very fuzzy, and is made up of very contradictory reports of government supporters and Free Syrian Army supporters. We'll do what we can.
What we do know is that the Free Syrian Army is now capable of occasionally holding serious bits of territory. The Syrian Army recently took back a big chunk of Damascus suburbs, and the rebels seem to have taken a suburb of Homs.
That said, I don't think this is going to be a territorial war like Libya was (this is closer to "everywhere at once"), nor as much civilian terrorism as Iraq (though that certainly is happening). It is definitely a wide-ranged insurgency, designed to keep the Assad government off its toes and on the defensive. And it may be working: the anti-Assad international community is increasingly excited about supporting it, though nobody has ponied up (officially) yet. (But more on their prospects later.)
It's still tough to figure out the current size of the FSA. The Army itself says their fighters are above 40,000--and with the amount of trouble they're causing over increasingly large areas simultaneously, this may be right. But it's hard to tell. And if they do have 40,000, they won't all be armed. Many will be in support and logistics roles, coordinating ambush-style attacks. But we know that the FSA is capable of hitting and destroying Syrian tanks (which are mostly sitting ducks in city streets against insurgencies), attacking major bases (like airfields), and even setting up roadblocks in areas near Damascus.
But keep in mind: the Iraqi insurgency, which was far larger, better-funded, and better-armed, failed against the US-led coalition and the burgeoning Iraqi military. That said, the Syrian army is not equivalent of the US army, but the will to remain is incredible. Like the Ghaddafi regime, the Assad regime is very unlikely to willingly go until near the end. Assad is very likely less delusional than Ghaddafi, and will therefore call it quits before death, but a prolonged insurgency won't be enough to cause him to voluntarily leave.
In short: the rebel opposition, made up mostly of the Free Syrian Army, is vast, increasingly organized, and has a safe haven in Turkey. It has serious staying power... as long as it is funded (the Syrian army has coffers to pay their soldiers; the FSA does not). We will see many continued months of insurgent attacks against the Syrian army, likely attempting to convince rank-and-file soldiers or even entire companies to defect. The Assad regime does not have total control on the ground, and this should be a matter of serious concern for the regime.
More to come on what this means with respect to the FSA's prospects for victory, but it'll have to wait until next time.