I have an idea (if I had a dollar for every idea I had... but that's another story) for a way to jump on the LOLCats bandwagon, but I wonder if someone can suggest a script (or a set of WordPress plugins?) that can support both the blogging and the user-submission aspect of the meme.
Give us some more info... Do you want to make a site about them, or do you want to blog, or do you want to make a site with thousands of images?
If you want user submission, you can easily have them sent to your email. You could use one of the many contact form scripts out there and add a simple upload function to it. It wouldn't be too difficult to setup. Are you thinking of something along the lines of what's over at icanhascheezburger.com where the user can create their image online? If so, that's a bit more hefty and would require some clever usage of the GD library.