to my knowledge, i don't think there is any limitation set by the server (as they are stored on the visitors computer).
However, why would u ever need more than a few? its easier to either use session variables (ie. 1 cookie that references a file on the server with many variables) or maybe a database.
An excess of cookies is simply studip because it is so difficult to keep track of what is what and also it is quite insecure.