I certainly don't think that paypal is perfect, but is there any alternative financial intermediary that works as well to assist individuals buying & selling online?
A buyer charging 3.5% or 4% extra to cover the fee is really no different than the many brick & mortar merchants that offer a discount for paying cash or an additional charge for using credit card. If you figure in the time and expense it takes to get a money order and the additional wait time to receive your goods, a 4% fee seems like a bargain to me. My only issue regarding paypal fees is not with paypal itself but with sellers that want to you purchase goods from them and pay with the gift option in violation of paypal rules and leaving you with no buyer protections should the seller not live up to his/her word.
If you are a seller and don't' like not being to transfer your money immediately, just get a paypal debit card which can draw on your funds. That is a heck of a lot faster than waiting for a payment in the mail, then taking it to the bank and waiting for it to clear. If you are worried about paypal reversing charges and pulling funds from your linked bank account or credit card you can, 1. use a special bank account or card for paypal use only and/or 2. conduct business in a manner that mitigates this risk.
As far as the paypal protection goes, I find it more pro-seller than pro-buyer. With a paypal dispute when a seller sends the buyer something other than what was described, the buyer must return the item to the seller at the buyer's expense before paypal will reverse the charges. A good seller, of course, will take care of the issue before the buyer proceeds with a paypal dispute. With a bad seller, the buyer gets screwed over using paypal protection, just not as bad.