You will not lose LINQ, you will lose LINQtoSQL. LINQ itself is more general, as it can be used in everything that implements iQueryable.
You are losing the SqlDataSource, not the big deal.
You lose the part of the integration that the server explorer does for you with the sql server, again, it doesn't matter.
As far as I'm interested, you are not losing anything very important, and you should not lose any of your .net knowledge. Most examples use the default sql server, but you can easily modify them to use a different database.
There are also some open source .net CMS packages that are already using MySql to watch cuyahoga
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