I use certified bank checks because I will not agree to Paypal's terms and conditions. I find it strange that anyone who has read them would. I obviously prefer seller to ship upon receipt (to some degree we are both taking a leap of faith), but I have no problem if the seller wants to take a day or two to verify or even hold out until the check clears.
As a buyer I would NEVER feel comfortable doing that, unless it was from a business who was established enough that I knew their reputation was worth more than whatever I was paying. I know being the buyer is a little off topic here, but I feel it's worth mentioning.