I don't care what you think, but the fact that yahoo has email addresses like email@example.com, or firstname.lastname@example.org, etc. - that's completely idiotic.
Why do I need to remember, besides the username, the yahoo extension? It's like saying "Hey, his name is James, but you need to call him James Jayjay before he answers".
I really don't care about Yahoo's history, but this should not exist. If it's yahoo, it should be "yahoo.com". I'm more and more inclined to forget about Yahoo completely. Really.