First off, awesome that you were reading my blog, and awesome that you like my book, and awesome that a post of mine sparked a thread topic! And by awesome I also mean thanks, I am very flattered.
On to the topic. As you can already see you've gotten quite a few different views on authorial intrusion (something, in case it wasn't clear in the OP's post, I do use in Alex). I should clarify that I don't think it is frowned upon as in "you shouldn't do this in good writing", but rather it appeals to very specific tastes. Like what IceCream said, it often suits a comic tone very well.
I find Lemony Snicket a good and bad example. He is a perfect example of an author speaking directly to the reader, but at the same time he is technically a character in the books as well. I think this makes his intrusion a lot more acceptable than, say, even mine. When I read books as a kid, and the author suddenly addressed me (the good old fashioned "dear reader" thing) I thought that that was so cool and it stuck with me. That's why I use it, I like it. Some however really don't. They want the story and, like others have already mentioned, they find an author suddenly addressing them takes them out of the magic of being totally immersed in another world. Totally understandable.
I also agree that if an author is going to do this sort of intrusion, it really should be consistent, and not just a few times. Otherwise it can almost look like a mistake, almost lazy.
But done well, I find author intrusion can be lovely, and very funny. But it definitely isn't widely loved. It is a very specific style of writing and will appeal to very specific tastes. That's why, I imagine, editors and agents caution against using it, because it isn't as universally loved, and to be honest, not that easy to do without it being obnoxious.
As ever the most important thing is to write a good story, and use whatever methods of telling that are most appropriate for it. You can do anything you want, as long as you do it well!