I hear ya, kedusha! Never done that, don't plan to - besides, from what I understand, it makes no sense anyway, since (within reason), dress size doesn't really say that much about girls.
And the only time I was told a dress size (without my asking), they lied by about 6-8 sizes, nearest I can figure (based on my admittedly limited knowledge of how sizes work). :D
;D
As an aside, when people call me about shidduchim, I don't even ask about looks - because that's something I need to decide myself. Someone once called me about a girl,
Me: "OK, can you give me her basic information?"
Shadchan: "She's blonde, about 5'6"..."
Me: "Uh, I mean like, where's she from, what seminary did she go to...you know, so I can find out about her?"
:D