tex4ht seems to do a pretty good job - it can handle complicated macros, because it runs LaTeX itself to produce a DVI file, and converts that to HTML. (I think it fiddles around with the styles to put \special commands in the DVI file, so it can recover the structure of the document.)

A good-looking Postscript file isn't the same as a good-looking HTML file, though, so in my experience the output isn't quite so pretty as a hand-written HTML file (it indents paragraphs, for example, as that's what the style says to do, even though most HTML files don't do that). I suppose changing the style a bit could fix that, but I haven't got round to trying...