I'd suggest using *anything* but Registry to store client variables, if you in fact need client variables. What OS is ColdFusion running on? If Windows, using Registry can over time bloat and even corrupt the Windows registry, especially if you have a lot of web traffic. If you are on Linux or MacOS, a flat-file registry simulator is used, which is highly inefficient for storing data.
Alternatively, use either cookies (if the amount of data stored in client variables is small and limited to simple values) or use a database.
-Carl V.