Most likely, the startup will go bust and you won't get anything. Even if it doesn't, I don't think they can possibly give you enough (unless it's Facebook or you are getting 50% of the company) which equates to months or years of your life that you can't ever get back.
My solution? Salary only and I take the salary and fund my own startup.
I wouldn't go so far as demanding only salary because it kind of implies that you are certain that the startup will go bust rather than _might go bust_. However, I definitely prefer as competitive salary as possible; I don't know about the rest of the country but working long hours in SF gets expensive (apartments, eating out, laundry services etc).
Most startups fail (and I've taken enough of the crappy deals to find this on my own), so I've become a skeptic, usually doing a better job of analyzing their ideas and connections. I end up charging my full rate (which to me is more valuable than the gamble of equity) and then using it as capital for my own projects.
Another issue is that it makes you a slave to the company. You don't want to leave because you want that equity. It's almost like continuing to gamble at a casino hoping for that next big payout.
A friend of mine wouldn't leave because he had equity..even when management sucked and it was a terrible place to work. The company didn't get their next round of VC funding and went out of business withing 8 months.
My problem is that it's too easy for the management of these companies to drive the company into the ground with terrible ideas..and you, as a minor stake-holder have absolutely no power to stop it.
My solution? Salary only and I take the salary and fund my own startup.