In general the offer seems low compared to offers I have seen though perhaps they are expecting you to counter. Good engineers are incredibly scarce in the valley and if you are good, you will almost certainly get a strictly better deal from other startups.

One publicly accessible data point is RethinkDB: http://web.archive.org/web/20100410043940/http://rethinkdb.c.... They are working on a very sexy systems problem (my concentration in CS is Systems and have no affiliation with RethinkDB) and they have a great team of investors (YCombinator, Andreessen-Horowitz).

Make sure the one founder is actually technical and didn't just build a bunch of simple iPhone apps. Ask yourself would you consider this guy/girl an equal on technical ability? 3 non-technical founders is a huge red flag unless they are in a very unique market. Also presenting the equity as a percentage of the options pool versus the entire company is fishy. What you care about is the latter and this makes it seem like they are trying to sell you rather than help you figure out what's best for you.

If you want to plunge into startups, absolutely apply to others. At the very least you'll have some negotiating leverage but I think you might find there are much better offers out there.