Are they hiring? Being the first employee at a company which is working on an idea you're excited about might be almost as good as being the founder.
The theory over there seems to be that the founders keep as much of the equity as possible, and pass it out the 1st/2nd/3rd employees in very small parcels.
Normally when I build a product here, it will be more of a 3rd/3rd/3rd split (Design/Dev/Business), or at least 20%/20%/60%.
I guess that means I'd prefer to be a founder, take on the extra risk (and the chance of extra reward!)