Jerry et al,
Strictly speaking, you don't rely on spacers to adjust stem height on threadless stems (once you cut the stem, you can't add spacer height) although the common practice is to have (3) 5mm spacers which of course can be reduced. Rather, you must decide on the length of the stem and the angle desired (don't forget, threadless stems are also reversible, so they are more versatile than quill stems in this regard). This requires more thought about the stem (especially for MTB applications) than traditional stem selection. I am not a fan of threadless stems (partly because they require more specialized equipment for installation and partly for aesthetic reasons) but, they do offer advantages over traditional quill stems, especially in the MTB arena.
As far as length is concerned, if you don't have to have the most high zoot stem $$ can buy, threadless stems are available (in 1") down to 60mm, and with the reversibility they offer, effective length will be versatile as well.
A big advantage of threadless stems/headset combos, is the adjustability of the headset out on the road/trail. A 5mm allen is all you need....that's handy!!! Try that with a Stronglight P-3; V-4 or S-7 or almost any threaded headset. Not to mention the routine maintenance aspect of the traditional stem/headset vs. threadless. How many times have I seen listmembers write in for suggestions on removing a "stubborn" stem?
Still raining here in Malta!!!
Chuck Brooks