That said, I tend to lean toward deepsand's feelings here. Mostly I am reffering to dealing with bolding/emphasising isolated words in larger blocks of text. To me, it is just quicker to open and close a <b> tag around one or two words than to close a <span>, start a new <span class..>, close that <span> and open the original <span> again. And by using <strong> I am using 5 more characters per incident. I don't think I'm being lazy, I just prefer the simplest means to an end. Of course, when it comes down to usablity, if browsers stop supporting the <b> tag, I would be forced to adopt the <strong> tag (and be happy doing it).
And that gets back to my question. Should I just go ahead and start replacing my <b> tags as I go so I won't have a lot of revising to do in the future?