It doesn't concern me much here or other 'community' sites, but with eBay, Craigslist, etc, the risk of fraud is just too great. I did some volunteer work with some anti-scam organizations and you would not believe the amount of bad checks and money orders out there. (I have about $5,000,000 worth of them) Many of these are impossible to tell from the real thing and the consequences can be disastrous.
If you deposit a check that turns out to be fraudulent, not only will your bank take back the funds (along with a shitload of fees) but they will most often terminate your account and ding your credit rating.
And don't be lulled into a false sense of security just because a check has "cleared". There's no such thing when fraud is involved and the bank can recover the funds as long as 6 years later in most jurisdictions.
Paypal fees ****, but I think it's worth the security.
I'll take cash, but lots of people are reluctant to put that in the mail.
See these? All fakes.