I think I first started following Bart in 2006 when I was learning about LINQ - A custom implementation of the .NET Standard Query Operators.
However it was this recent post on C# 4.0: Co- and Contra-Variance for Generic Delegate and Interface Types that prompted this 'recommendation'. It's a perfect example of what I like about many of his posts - I learned a lot! Some of the '3.0 examples' he mentions are just the sort of thing I've noticed, wondered about and worked around before: but Bart provides the "language" and "reasoning" that explains why... sure I've probably heard the terms co- and contra-variance before, and I can understand at some 'high level' why
IEnumerable<Person> people = from Student s in db.Students
where s.Age <= 25
doesn't (currently) work, but Bart's discussion and examples feel just like the 'developer watercooler' type conversation that might take place amongst developers at work - and suddenly I understand the concepts a lot better.
I enjoy reading (and re-reading, just to fully understand them!) Bart's posts, and highly recommend them.