Anyone that I've talked to about SharePoint 2010 knows I like MySites. I think everyone should have a MySite. My cat has two. Unfortunately not everyone agrees with me. About once a week I get asked, "How do I disable MySites? I'm a big meanie." I figured it was time to put this into a blog post, so I don't have to fight back tears every time I have to explain how to do this. I'm tearing up now as I type this.
First, go into Central Administration and click Manage service applications
Then click your User Profile Service Application and click Manage
In the management screen, click Manage User Permissions
You'll get a window that looks like this:
By default all authenticated users have permission to "Create Personal Site." To keep people from creating them, remove that permission for both authenticated users entries. Users will no longer be able to create MySites. At this point you can add users or domain groups to the top of the screen and give that group permission to create personal sites. The recommendation I usually give it to create an AD group for people that can have personal sites. Then as you decide to give users permission to create personal sites, you drop them into that group.
This can be done in PowerShell, too (I think). I'll figure it out and blog it later.