[sdiy] Tap Tempo?

[MED]

How would one implement a tap-tempo?
For elements that are run off a clock like a sequencer, i could imagine a
PLL clocked off of a debounced switch... most likely first-order or more to
avoid "sudden change"/phase problems.
But how would you make a delay to use tap-tempo? Wouldn't this cause
horrible pitch fluctuations as the clock runs up and down?
Is this how standard delays do this? It seems like a really poor
implementation...