I actually agree that eBay has become a little more impersonal, and somewhat to its detriment. I don't necessarily want to start life-long friendships with my buyers or sellers, but as a seller, I ignore eBay's push for no communication and send every single buyer a direct, personalised message after purchase and payment.
It's very straight to the point, and along with a thank you, contains only information I feel is relevant and not really provided by any of eBay's automated emails (I've switched off all the ones I can), but the most important reason I do it is because it opens up the way for direct communication if something goes wrong, and to this date only one person has not gotten in touch with me about a problem before leaving feedback (and the neg was because the item was as described).
But all that being said, I'm not so sure a 'mark as received' button will make things less impersonal from the buyer's perspective - it would be an eBay function, and would perhaps exclude the sense that a buyer is communicating something to a seller.
