A new feature was added to the re-linq front-end that makes IMethodCallTransformerAttribute and MethodCallTransformerAttribute obsolete: MethodCallExpressionTransformerAttribute and AttributeEvaluatingExpressionTransformer.IMethodCallExpressionTransformerAttribute. These should be used instead. (This includes changing the interface implemented by the transformer class from IMethodCallTransformer to IExpressionTransformer<MethodCallExpression>.)
Note that this means transformations will now be executed earlier in the query processing. This enables transformers that return expressions with query operators (e.g., translate a "Friends" property to "RelatedPeople.Where (p => p.IsFriend)"), which was not previously possible.