memcached is a distributed in-memory object cache. It's basically a big distributed hashtable written for a simple practical purpose: to stop livejournal hammering MySQL quite so heavily.
The first thing people generally do is cache things within their web processes. But this means your cache is duplicated multiple times, once for each mod_perl/PHP/etc thread. This is a waste of memory and you'll get low cache hit rates. If you're using a multi-threaded language or a shared memory API (IPC::Shareable, etc), you can have a global cache for all threads, but it's per-machine. It doesn't scale to multiple machines. Once you have 20 webservers, those 20 independent caches start to look just as silly as when you had 20 threads with their own caches on a single box. (plus, shared memory is typically laden with limitations)
There are Perl, Python, Java and PHP APIs.
why aren't you writing personal blogs anymore. they are kinda fun to read, even when you attack me, mr.fishbowl.
Anyone wishing to only see my nerd-posts can use one of the "nerd" RSS feeds listed on the right-hand side of the blog's front-page. This is the feed that is syndicated on Javablogs, and will only contain posts related to computers, the Internet and online culture.
Anyone wishing to see only personal stuff can follow my Livejournal, which is linked from most pages of this site. (Note: the Livejournal duplicates posts from this site, so there's no need to follow it if you already follow the full-feed fishbowl).
I might also add (and apologies to Chiara in the extremely unlikely event that's really her) that the "impersonating other bloggers in comments" gag has been done to death by now. It was funny for about a day, now it's descended to the amusement value of those recurring slashdot jokes. Let it go, people.
[It turns out it actually was Chiara. How bizarre.]