I always read rejection mails - I like to know what I screwed up today, if only so I can screw up something different tomorrow
Seriously, feedback on what I'm doing wrong is always very much appreciated. Acceptance mails I just glance at - I've never yet seen one say anything significant other than "you're accepted".
The points about length of backlogs are well made, though. I've not had time to build or submit any sites in a few weeks due to some family commitments, but I'm still getting a fairly steady stream of acceptance mails for sites I submitted four months ago. Of course, I'm happy to be approved there at all, but if I'd been building sites all this time instead of doing family stuff I would have built a fair few sites by now that I simply wouldn't have submitted to those lists because I figured they were either dead or didn't like the sites I made.
With that in mind, I think it's always good for a list to send out acceptance / rejection mails. Sure, some folks might ignore them, but for the rest of us its a helpful indication of what's working and what isn't.
Rob.