I like your forum topic title, very eye catching, if a little dramatic.
It is very wise to be aware of what you are downloading, but also to understand who is asking you to download. Your teacher has been using and testing the applications and so it would be pretty common sense to believe
a) there is going to be little risk as Ed's reputation is on the line
b) if Ed is using them then it's been tested for anything nasty.
So saying that it really is a personal responsibility as others have said, to ensure you are not using soft passwords.
Web 2.0 applications makes using the tool so easy to use that it can seem that there is little substance to the security side. But remember a lot of reputations (and incomes!) are on the line here and the stuff being taught is really middle of the road safe and secure.