One of my pet peeves (and it is Microsoft's fault for such a terrible naming scheme) is how people use LINQ interchangeably with LINQ to SQL. LINQ is a language feature used by other frameworks (LINQ to XML, LINQ to Objects, etc). LINQ to SQL is an ORM.
Mostly the fact that I can "query" any data source (an array, a file, etc) in the same way I query a table. Lovely.
DataMapper is great. Doctrine is good. Linq is my fave.