Is using <a href="#"> a good idea?
That's the usual trick. But in addition to not conforming to specifications (since "#" is not a URL reference that complies with URL syntax, still less is there any meaning assigned to it in the specs), it has the nasty effect of taking to the _top_ of the page on most browsers (and perhaps somewhere else on other browsers). This of course matters only when client-side scripting is not enabled - or when the author forgot to terminate the scripting code by return false. :-)
This is safer:
<a name="this" href="#this">...</a> where "this" is any name you like, different for different <a> elements on the page. If the link is actually followed, it then takes to that very same location.