At my startup, we have talked about this issue several times about how we can fairly compensate employees for their contributions to the company. Our company is a bit different in that we have a lot of young employees who are eager to learn and believe in the vision rather than people who maximizes reward and minimizes risk. Because of our employee makeup, we're adopting a revenue sharing plan. In my eyes, that's as fair as you can get: getting a ton of experience with the latest technologies for a temporary cut in pay. As a lot of commenters have said, it really depends on your situation, but I believe the reward is potentially great if you're a young engineer who's seeking a long-term reputation as a good programmer.

(And for those of you who think I am mad, my company is great in that it's fun, the work is extremely challenging yet exciting, and the vision aligns with my own personal vision. It's my dream job.)