Els said:
As far as the guessing game goes: I think he does mean the
infamous white space below a form (usually noticed when putting
a form inside a table cell), and that he made a minor mistake in
the CSS so that the margin-bottom:0 got ignored.
That would be my first guess too.
My second guess would be that in this case the form does not appear inside
a table cell but elsewhere. Then it has both a top margin and a bottom
margin by default, as you can see if you view a page containing
foo<form action="zap">bar</form>foo
For some odd reason, popular browsers by default suppress the top margin
but not the bottom margin.