EBay is currently laying it heavy on with PayPal in the sense that ALL listings will soon HAVE to have PayPal as an option and some will have to have nothing but PayPal.

That would seem to indicate that this sort of promotion is on the cards, and they are more likely to send it out as an encouragement to use PayPal than anything else.

IF the invitation is a code for PayPal then you should be able to use it no problems. Buy off someone who takes PayPal, and at the payment screen you will see a box for entering a code. Enter it and it will take money off the total - but the seller will get full payment, PayPal meet the value of the code.

I've had the odd one off PayPal and eBay in the past, usually via email, but because it is just a word code that you enter in PayPal, there should be no security risk.

My advice, use it whilst you've got it. So if you want that 'something' but don't want to pay the full price, now you have a tenner off!