[arscan]

If a service prevents me from signing up with whatever email address I want, I won't be using it. It's one thing to discourage weak passwords, as that's a common mistake for people that don't know any better. It's another thing altogether to deny signing up with something like this, as they clearly will know the ramifications of doing so.

[jacobn]

I have a website that gives freebies (=$$$) to new signups, so allowing throwaway accounts makes people do things like sign up for 100 accounts.

Not giving freebies is of course an option, but then there is goodwill lost on that end instead.

It sucks both ways. At least I don't spam my users, but they of course only trust that assertion so far and I certainly don't blame them - there seems to have been a significant rise in email marketing in the last 6+ months - probably some annoying YC startup or two making it much too easy for sites I signed up for at some point but really don't want to hear from send me email... Tsk, tsk ;)

[LiveTheDream]

Then just give the freebies to non-throwaway accounts. Now your users still have a choice, and you don't lose any goodwill (obviously, explain that throwaway accounts don't qualify).

This is on the same level as adding a CAPCHA if someone comment looks like spam.