Well-said. Founding a startup can be lucrative. Joining someone else's? Unless you're VP level or above, it's generally not a good move financially speaking. (If you're a non-founding first programmer, demand a VP-level title, investor contact, and the right to attend board meetings-- voting rights are probably not an option. Titles mean nothing early on, but you want to lock that in to make it clear that you're not a JAP, where JAP means "Just A Programmer".)

For every other case, the rules for joining a startup are the same as for any other company. Join if it's a promotion, and if the gains outweigh the risks. A lateral move (salary wise) into a startup is fine, but if there isn't some level of technical promotion, at the least, it's not worth doing. Also, the mere fact of it being a startup does not a technical promotion make; a lot of these bubble startups are using the worst kind of enterprise Java.

As I said in another post, what's actually overvalued in 2012 is not startup stock, which probably reflects an accurate EV for these new ventures, but subordinate positions within startups.