I've loved games and puzzles my entire life. For the past few months I've been part of the playtesti g team of a game called "Liberty or Death-The American Insurrection". For specifics about the game from the designer and the company check out their Facebook page or boardgamegeek.com
So, what does a playtester do? Playtest! Our group suggests changes to rules to make the game easier to understand, or more thematic. We also suggest changes to game mechanics to make the game more balanced, replay able, or perhaps to better model historical what if. We might also suggest changes to the components of the game. In the end, it's not our decision but the designer and developer are genuinely interested in our feedback.
The last few Friday nights have me perched on my computer, teleconferencing via Skype, for hours.
Great fun and a great experience.