Irritatingly BoB (despite previously lauding the fact that they didn't) and Fictionwise seem to have started charging a transaction fee for small purchases (i.e. $5 or less).
I just bought at $2.58 book from Fictionwise using Paypal and was charged $0.50 "transaction fee", making the purchase more expensive than it would have been from Amazon. That's a 20% mark up.
A recent $2.86 book at BoB also using Paypal gave rise to a $0.25 fee - almost a 10% markup.
Even more annoying is the fact that the possibility of a transaction fee wasn't mentioned anywhere on the site before I purchased.
Not sure if this is just for Paypal or all payment methods.
This will obviously scupper BoB's attempts to undercut everyone else, especially Amazon who don't seem to charge extra no matter how small the amount.
Worth bearing in mind if you're comparison shopping...