Note that the Harry Potter spoiler, the penis/NYT edit, the FOX edit, and Oral Sex edit disappeared in about a minute, sometimes less. Unfortunately FOX's On the Lot lasted a stunning 13 minutes. (Go to Newer Edit, then look at the "Revision as of" line to see the time difference)

The other edits, especially the edits that aren't as obvious as the cliche LISA IS A LESBIAN!!!, sometimes sit around for a while. I removed some vandalism from the Lord of the Flies page that had lasted for weeks insisting that Roger was a perfectly little angel (he's really a symbol of sadism).

There's a reason these edits usually disappear so quickly. The Wikipedia community has set up many mechanisms and tools for dealing with vandalism. Among other things, anti vandalism editors are assisted by tools that ease checking new edits. VandalBot, an automated program, catches simple vandalism such as blanking pages. Now Wikiscanner is yet another deterrent. The system isn't perfect, but it's much better at protecting Wikipedia than many critics realize.