Many comments seem to focus on traditional GET requests in which case long URLs are usually a smell. But there's a rather new requirement in the web that conflicts with limits on URL length: the use of modules for front-end JavaScript code. The best practice for modules is usually expressed as:

1) Write small modules 2) Concatenate scripts

If you try to automate module concatenation then you'll get URLs like http://example.com/combo?foo.js&bar.js&baz.js, which combined with "write small modules" can mean a long list of small modules that easily reaches 2000 characters.