Heh a lot of you guys are wrong saying that MO is pretty much secure if it is from the Postal service.
MO can be forged, but the chances of that are slim; however, there isn't really a way to verify it is genuine on the spot.
For USPS Postal Money orders they can check the number to see if it is a batch of potential fake MOs, but no guarantee.
As for cashing/depositing the MO it takes anywhere from a few days to several weeks before it clears your bank.
I would treat MOs in this order. MOs > Cashier checks > Personal checks. I don't even accept MOs anymore due to the risk of it being fake unless it was some kind of wire transfer.
There are services these days where you can have the user pay you money using his/her credit card.
I used to use BidPay which was owned by Western Union as they had pretty good service. It was easy to receive money from another person, bad credit cards are usually caught within 2 days (sometimes a couple hours), and the funds could be directly transfered to your bank account.
Right now BidPay is owned by CyberSource and I haven't signed up to this new BidPay yet. I'm currently waiting for Google checkout to become more recognized and worldwide.