I.e. don't paint grass on grass, or wool:red on wool:red
Because: it adds very rapidly to the logblock/hawkeye database, if the user is holding rightclick and spraying back-and-forth. For example, if grass is selected, and the user is spraying it around a mountainside.

Release 0.3 has the fix
http://dev.bukkit.org/server-mods/toolbelt/files/6-tool-belt_0-3/