The last time I've checked, the man page format (nroff/groff) didn't have a 
specific tag 
for underlined text, that's why underline doesn't work in man.

If that has changed and now man has an underline tag, please let me know.

Here is what I can find in the Nroff/Troff User's manual
(http://heirloom.sourceforge.net/doctools/troff.pdf)(p.40) :

----------
Request Form: .ul N
Initial value: off
If no argument: N=1

Explanations: Underline in nroff (italicize in troff) the next N input text 
lines.
Actually, switch to underline font, saving the current font for later 
restoration;
other font changes within the span of a ul will take effect,
but the restoration will undo the last change.
Output generated by tl (§14) is affected by the font change,
but does not decrement N. If N>1, there is the risk that a
trap interpolated macro may provide text lines within the span;
environment switching can prevent this.
----------------

Hope this help.

++ fredg

I've looked at this, the problem is .UL seems to be for paragraphs (or lines), 
so while we can write \fBbold\fR for bold, I don't find a specific syntax for 
underline.
.ULunderline.RE. is not workink, and not \fULunderline\fR either.

Btw, 
.UL
underlined ?
RE.

doesn't underline the text, and \fIitalic\fR is underlined in the man pages, 
but italic in the postscript output.

As there's is no italic font, man pages use underline to mark the emphasis. If 
you test html output with some text browsers, you will have sometimes the same 
behavior.