read through the FB ad guidelines, but still not sure about toolbars, are they allowed?
I made a lot running toolbar installs around 3 years ago, still wondering to this day why my account wasn't banned.
I wouldn't run any download type offer these days unless it's past some sort of a gateway.
Example: Email > Day 1 copy > Day 2 toolbar download
Definitely do a gateway. I ran a toolbar via a fan page a few years ago. Promoted it as "Elf yourself" around Christmas. Users would "like" the page then I used FBML to show the likers my optin. Once they opted in, I sent them to the offer, then followed them up with a few games. It did a few grand in a few weeks then died off mainly because of the seasonal nature of the fan page. If you hit the right angle that had year round appeal, there's no reason why you couldn't make consistent money all year.