OK so I know none of these words mean the same thing. Obvs. But I am grouping them together because I hate them all in the same way. I feel like people calling things "meta", "web 2.0", and as possessing or resulting in "synergy" all sound like douchey poseurs.
The difference, I feel, is in the setting in which the words are used. It's sort of a high-brow to low-brow scale, like with Old Navy, The Gap, and Banana Republic. They are all selling the same shit, but for varying prices and levels of status points. So Web 2.0 I think would be Old Navy, becuase it's all mainstream and mall-ish. It's all about bright colors and accessibility. Synergy is The Gap, with its emphasis on streamlining and minimalism, and trying to make a Clone Army.
Rounding out the METAphor (lolz) is Bana Republic. Saying something is "meta" is a safe and undergrad-sounding way to say you don't understand it, and buying Banana Republic says that you have enough money to buy nice clothes, but you don't actually understand style and would rather someone else think for you. People who call things meta often buy clothes from Banana Republic and then say they are from Value Village. Probably.