RFC does not specify a limit, but IE limit is currently 2048 :
other browsers may be shorter.
Microsoft Internet Explorer has a maximum uniform resource locator
(URL) length of 2,083 characters. Internet Explorer also has a maximum
path length of 2,048 characters. This limit applies to both POST
request and GET request URLs.
If you are using the GET method, you are limited to a maximum
of 2,048 characters, minus the number of characters in the actual path.
However, the POST method is not limited by the size of the URL for
submitting name/value pairs. These pairs are transferred in the header
and not in the URL.
RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1," does not specify any requirement for URL length.
But we must also respect Tim Berners Lee's statement: "Anything you can't pack into a reasonable URL length is probably not good candidate for GET anyway. "
So my recomendation: keep it short!! 