If you are being offered equity as part of your compensation, what's really happening is that you are being asked to invest in the company. You should evaluate that using the same criteria you'd use when evaluating any other potential investment. If it's a startup, this is also a very high-risk investment, more on the side of gambling than not.

My personal stance is that I ignore equity components of employment offers when evaluating the offer. I prefer to separate my investment activity from my employment. But that's just me, and different stances are entirely reasonable.