There is a limit on the length of a GET parameter. It's best to do it via a POST instead.
No their isn't. The only way your limited is by how many characters the browser can handle. For most browsers this is a few thousand which means no problem. The problem is with some older versions of IE which can only handle 2,083 characters but that's still a shit load of links. Currently his link checker stops at 75 links. 2,083 characters is at least 100 links so your fine.
Although it's old it's a good reference as most modern browsers will have no problems and it's the older ones you need to worry about. http://www.boutell.com/newfaq/misc/urllength.html
I've built this using this idea and have it working on a site fine. It works perfectly and is incredibly fast.