IMHO, if you do a startup, do it as a founder, or join after Series B, from a pure risk-rewards perspective.
You should seriously consider writing a "Don't Let This Happen to You" piece (a la Philip Greenspun) and posting it here to save others from the same fate. Change the names (including your own) if you like. A post like that could be the single most important thing some hackers ever take away from here.
Although on a cautionary note, I'd be careful what I post here, because it does tend to get picked up. Comments I've made got picked up by ValleyWag, and that's almost never a good thing.
To be fair if you were an employee, i.e. you got paid well I assume? there was less risk on your part relative to the founders. So your equity should be a fraction of what the founders took in. Why would it be otherwise?
I was responding to ojbyrne's comments that being a founder is not all hunky-dory since (s)he ended up in the same spot. I suggested at least (s)he got better equity being a founder and that is a big deal.
And I still think for a risk/reward outlook, either being a founder or playing it safe until after Series B are the two extremes and are both high in the value / risk ratio.
What would really matter for my ego is what piece of the pie I get in the end, although, in your position, it sounds like that's a hard area to negotiate, too, since said "semi-famous person" is adding all the value in the very beginning (before any code is written). This is probably faulty logic to base your equity on, since your piece should be proportional to the value you add at acquisition.
And I don't think that Kevin added all the value in the beginning. He was significantly less famous at that point, and in fact was about to become unemployed. Many of his coworkers tried to launch sites around the same time, with nearly as much fame, and they all failed.
There was a lot of luck.
I haven't heard about "management" and "non-management" equity, sounds like a cheap way for sleezy MBA types to hoodwink hackers out of money. Could you explain in two sentences how liquidity works? I assumed everyone just cashes in their stock when an acquisition (or IPO) happens.