I'm aware that the SQL Server 2008 R2 Express was limited to 1 CPU and 10 GB Databases. It's not clear if Microsoft bumped those numbers up to be more reflective of 2012. I looked at several places but I still don't have a clear idea. Yes, I understand 2012 is not yet released but I have to assume it's software performance requirements are already set.
Now that it's been in release mode, there's more information available on SQL Server 2012 Express. It looks like you're limited to:
As far as I am aware there has been no official announcement of the capabilities of SQL Express 2012, although I have heard rumours that it will be the same as 2008 R2 (1 CPU and 10Gb database limit).
Microsoft have released specifications for the standard and enterprise editions.
Please refer to this page:
http://msdn.microsoft.com/en-us/library/cc645993(v=SQL.110).aspx
You can't assume this - the limits of the Express Editions are not technical by nature. And as something specified by marketing, it can change any time - shortly before the product's release or even after that, where the updated code gets distributed through a service pack.