I don't know if this has been brought up yet, but I was giving an ING referral to a friend today and noticed that ING now requires the friend to make an initial deposit of at least
$250 to be eligible for the bonus(es).
It's still a nice bonus, but will cut down on their perceived "abuse" of the system so far. (you say to-may-to, they say to-mah-to type of thing
)