[Deceptor]

Host - I can see that occuring the first time it caches, but when it calls from cache it fixes itself, if you're continually setting that issue, your cache is not working right, check your vB Optimise debug messages in vBulletin Debug info (you need to enable it). Regardless i will resolve the issue where on first cache the background is odd.

veenu - Depends on the module, if the module is simply pulling a template, there won't be much impact, but if it's doing a lot of php processing then yes, since it'll save all the need for that processing.