I suggest to improve MongoReplyMessage<TDocument>.ReadFrom(BsonBuffer) by preallocating a list of documents, since its size is known, and doing it after error checking (so we don't allocate anything if cursor died, etc.).

— MongoReplyMessage.cs.orig Thu Jan 27 18:36:48 2011
+++ MongoReplyMessage.cs Thu Jan 27 18:36:55 2011
@@ -74,7 +74,6 @@
cursorId = buffer.ReadInt64();
startingFrom = buffer.ReadInt32();
numberReturned = buffer.ReadInt32();

• documents = new List<TDocument>();

var settings = new BsonBinaryReaderSettings

{ MaxDocumentSize = server.MaxDocumentSize }

;
BsonReader bsonReader = BsonReader.Create(buffer, settings);
@@ -89,6 +88,7 @@
throw new MongoQueryException(message);
}

+ documents = new List<TDocument>(numberReturned);
while (buffer.Position - messageStartPosition < messageLength) {
var document = BsonSerializer.Deserialize<TDocument>(bsonReader);
documents.Add(document);