D that is excellent idea for a plugin.
One thing to think though is that some users might want to run several instances of xlobby on same OS-installation (not necessarily simultaneously) and mayby have them use separate initialization information or persistancy domain for them and since register is kinda global data storage, it might be advantageous to some if u would offer regular file as storage possibility as well.
That said this comment is made without testing the plugin (my htpc still offline

) so if my asumptions are invalid and u already adressed several installations problem by for example using different heap in registry my apologies...
* failed in attitude check as usual *, read on with own responsibility.
i would have named this Xpersistant though

to stress the point that its also possible to write the registry and not just read initialization values from there.