Unixkcd is extremely convenient when browsing the comics one after another, so allowing to save a specific strip to your computer would be really nice. It shouldn't be too difficult to implement. [save + path]
I like the motivation behind this idea. I think we could have a "save" command that writes the current comic to a cookie, and perhaps a "load" command that gets you back to your saved position.
Or perhaps, we could just do this automatically, and when we detect that the user has a saved position, give them a "would you like to resume where you left off? [y/n]" prompt...
You can have the server return the image as an attachment so that the browser prompts to download (chrome will do it without asking). For saving your spot, though, chromakode has the right idea.
In response to sgbeal:
Can't java read what web browser is viewing it? This would allow an if...else tree to save using different methods. I use Firefox, so I can just right click an image to save it, but if it makes people happy to save images using uni.xkcd.com, then they should be allowed by whoever writes the code.