I agree with the Head Heeb:
The size of the Hizbullah and opposition demos should also put paid to the theory that either side was manufactured ex nihilo by foreign interests. It simply isn't possible to mobilize crowds that size in a nation of four million without genuine popular support.
The Hizbullah demo was not 1.5 million and today's was not 1.2 million (the highest number I've read for both.) Lebanon is a country of maybe 4 million so these numbers should be dismissed out of hand. But either side -- if they are entirely opposing sides, which I'm not convinced they are -- is definitely drawing around 20% of the population, which is unheard of anywhere in the world as far as I'm aware. A lot of it has to do with the geography and demography of Lebanon: it's a small country with decent roads (although the traffic jams on the already packed coastal highway must be insane these days) and several large population centers. And, perhaps most importantly, it is a country where people are highly politicized. This is why you see a fifth of the country on the streets at one time there but not, say, in Egypt.
Mass media man Abu Aardvark zooms in. Clever.
The Agonist has many links, including this one to a Robert Fisk story saying the UN is about to say the Lebanese and Syrian security services were behind Hariri's death. That link is pay-only, but you can read about it here.
One more thought: I have no way of knowing this, but maybe some of the people on the streets at both the "pro-Syrian" and "anti-Syrian" demos were the same? It seems to me that there is a lot of common ground on both sides, despite everything.