Just in case something useful arrives back at that address, you can read it on the web -- or, better yet, you can subscribe your aggregator to the RSS feed associated with the mailbox, and see new mail arrive whenever you catch up on your feeds.
It also makes a decent voyeur pastime -- just guess a name and read.
I wouldn't recommend using it for your DynDNS account though.
(Mailinator did this first, but their interface is overloaded with things that are not mail (why are there photos of people taking up so much room?), and they do not offer RSS reading of mail, which is the killer feature of this sort of thing for me.)