i've experienced foot-washing several times. never in a church service - it is quite meaningful when in a small group with people you feel close to. once was in a youth group, once in a small Bible study group, another time we washed one another's hands rather than feet. it really felt humbling and intimate - took a lot of trust - both being the washer and the washee. i think it would be sort of weird with strangers or people you don't know well.
"That you are here - that life exists, and identity; that the powerful play goes on and you may contribute a verse. . . What will your verse be?" Robin Williams as John Keating in "Dead Poets Society"