This is a small note, but important, ohhh SO Important.

Any file inside of your site whether it be in a document library, list, or root folder, must not contain any special of the following special characters. If they do then when you attempt to activate your site solution, it will error and you will not be able to create a site with it.

? " # % & * : < > \ { | } ~ [ ]

The first bunch are not allowed by SharePoint but the last two “[“ and “]” are and will cause you a problem during site activation.

Now you ask why does it matter – well these files are separate physical files inside of the WSP. As such when it tries activate the solution, because those are invalid characters, an error occurs during extraction and wala, activation fails. Sucks I know, but I’m sure it will be rectified by MS before RTM.