Terrific article by Fred Wilson on how much equity an employee should get in a startup. This is a question that I get a lot from friends who are going to startups. It's always really tough to answer, especially because my age group is typically at the Senior Manager, maybe Director level. There's less visibility into equity grants at those levels and often the company hiring them won't say how many shares are out or what the valuation of the company is.
Fred's methodology relies on "equity dollars at work" and it's pretty solid. Read his post because it's a little too complicated to summarize here. Again, some of these inputs will be hard to get if you are interviewing but push for them. You should be able to get some ballpark figures.