I have a masterpage (copy of v4.master) and I added a link to a custom css. when I create a new site it does not pick up the correct master page. How do I fix this? thanks
You can turn on the Publishing feature for the Root site and in the Site Action -> Site Settings -> Master Pages you will see a screen like below:
Here you can specify to inherit the root-site master page for sub-sites!
Also, if its just a CSS that you have used - at the bottom you can see an option to Specify a CSS to be used by this publishing site and its sub-sites!
Read answer from David-Andrew-Smith on this URL for detailed info
Hope this helps