Snap, I agree, and I too do occasionally have recourse to the old 5x table (typically once every six-months, when I'm in the simulator jumping though the hoops of the LPC / OPC checks) and / or in conjunction with the 3x height your height rule especially during 'visual approaches' with either runway DME distance (or an equivalent point via the FMC's 'fix' page) available.
Now the DME on the RDMI's which I use only give the slant range Nm to the tuned nav aid - and not Groundspeed (that is displayed, incredibly acurately, on our Electronic HSI's).
That said, I suppose that if you're using either a Bendix/King (e.g. KN62A / KN63 / KN64 / KDM706A / KTU709), or NavCom products, etc, all of which are typically found in light aircraft (e.g. I used to have a KN64 in my own spam-can).... then you might well indeed have a combined (or even single) distance and (or) G/S display.
In any event, and whilst ball park figures are a great aid memoir, I'd caution against trying to do math in the kind of weather that I had today, during an approach through the mountains situated north of Malaga, i.e. it was embedded Cb's / Heavy Rain / Turbulence / cloud base only 100' above the Cat I minima / plus a steeper than normal glideslope.
Accordingly, imho, I still reckon that you should read your groundspeed from the electronics, and then compare that with the V/S required to maintain the glideslope from the relevant section of approach plate which is (should be) right in front of you - it then all becomes a veritable 'no brainer', so leaving the old grey matter to cope with more secular activities, like, flying the aeroplane !
Also I'd still suggest that you should be cautious (particularly in rough weather; see above) about following a barometrically derived VSI, i.e. instead of one that's derived via electronic means, e.g. from the aircrafts INS platform(s) and which therefore is an instantaneous measure of the aircrafts up'in and down'in.
Ps. (and hence the edit) I must correct what I said above, in that 'Hystersis' is actually of Greek origin, e.g. husteresis from hustereo (be behind), from husteros (coming after) - uhm, I never really did get to grip with the classics !
[This message has been edited by Devils Advocate (edited 03 May 2001).]