Text Effects
Use of bold and italic text on the web works differently from other mediums. Search engines will regard words and phrases in bold or italics as being slightly more important than others on the page. For this reason, all key words and key phrases should use these effects where possible. They can still be used to emphasise particular points unrelated to key words if desired or necessary but try to ensure at least the first instances of your keywords have one of these effects applied.
Underlines should be avoided unless absolutely required. Because the majority of websites use underline to denote links use of underline for non-linking text can unnecessarily confuse users.