Thanks for the advice so far. The data that I want to store isn't anything critical - there are five filters that users can set up for searching / viewing data, and it's these settings that I would like to put in the cookie. The cookie data would be compared against the list of valid parameters, so if users did have the inclination to tinker with the settings, the worst they could do would be to set the maximum possible filters, which you can do validly by setting those filters using the cgi.

One possibility if the data structure is too big might be to have a couple of cookies, as there are some filters which only apply to certain aspects of the program. I don't really want to be setting huge numbers of cookies if I can help it, though.