Thanks for all the excellent info on how ff miles are blocked on Priceline. I've seen people with Priceline boarding tickets that have Priceline typed in bold black letters on it.

Miles using Priceline fixed price option
 

Recently I needed tickets to Cancun. Checked all the usual places and found prices very high. Then checked Priceline to see what it had to offer. Did not use its bidding process but picked a scheduled flight at $150 less than I could find elsewhere. Buying 5 tickets, that was a lot of money.

Got booked on Delta. Got a Delta locator number. Went in and redid seats and entered FF #s. Just checked back and FF #s are still there. Haven't flown yet so cannot be sure I will get the miles but it looks good. If not, I lost under 4000 miles per ticket but saved $150, that is over 3 cents per mile -- not bad.

The non-bidding side of Priceline works just like any other portal, so the fares are eligible for miles.