We run a fairly large multisite install and this plugin will allow clients to see each others timthumb scripts (and fix them!). This may or may not be a big issue, but I can see how it could cause some disruption.

What we did was install the Restrict Multisite Plugins plugin and this will allow you to restrict the install of the Timthumb Scanner plugin on your parent site only, so then none of your clients will see it.

Just thought I'd throw that out there for any multisite users.