Thanks Spence.
After looking at the KB and digging around further in the registry, it looks like you can limit the number of log files created. Default is 100 x 20Mb (which is actually 200 x 20 Mb as there are .log and .dat files!)
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\SWSvc\Parameters\VMwareEsx
Adjust the DbgLogFiles DWORD as necessary.