Now I know what you are thinking... who in their right mind passes so much information in the querystring that it would reach the upper limits??? I agree with you, but it is currently out of my hands.
Building "widgets" and "plugins" for commercial sites that expect to be able to "remote authenticate" can be quite tricky... especially if they are built on 4th party CMS's that decided to build their own proprietary server side scripting language (that remotely resembles classic asp)...
Okay, long story short, I am passing variables to the remote authenticator via POST variables... that software is then authenticating the users and moving all of those POST variables to the querystring as GET variables to return the user back to the clients CMS where we then process their data... I know, I know, it's an incredibly complex mess, but until the CMS is able to provide us with methods to read and write cookies, we are stuck with it.
So, it turns out that although this specific case works fine with FireFox and even Safari, it breaks in Internet Explorer (what a surprise =). Because of this I did some testing... and here are the results:
Browser version querystring upper limit
FireFox 22.214.171.124 8182
Safari 2.0 8184
IE 7.0 2047