One of my pet peeves is the wanton overuse of emphasis. Partly that's because I read italics specifically in a whiny, supplicating voice and it ruins the scansion, but also it's because when everything is emphasized, nothing seems truly emphatic. This writing habit (and reading burden) seems particularly endemic among forum posters who write way too much and amateur bloggers. In other words, formatted text was a mistake.
I think what Elmore Leonard said about exclamation points is applicable here: "You are allowed no more than two or three per 100,000 words of prose."