People should stop using bold and italics tags in their comments on all discussion boards. These tags are like cursing: can be good to bring home a point from time to time but far more often are simply crutches to make up for the fact that the author can't effective express himself/herself.
Bold has no semantic meaning. It is meant to denote emphasis. Unfortunately this is used as a substitute for the lack of ability to use words for emphasis -- to use an idea to drive a point home.
People post simplistic messages. Bold text makes a simplistic message more noticeable. If you're going to be a simpleton, it's probably better not to advertise it quite so much.
Italics: used to denote publication titles and the like. Also used as an alternative to bold (see above). If there were a "publication" tag -- for example -- there would be no need for an italics tag in 99.9% of all comments.
Leave styling to the stylesheets and the rest to semantic markup.
Oh yeah, I almost forgot; Learn how to spell!