|more useful options|
Translation is always the fastest if you can use it, at least that's my experience.
One thing to consider is that the alternatives suggested remove all whitespace -- the join/split just drops leading/trailing whitespace and squishes all "extra" in between down to one space -- provided you join on ' ' and not '' -- you need to do more than one regex/translation to accomplish the same thing.
The simplest (to read) equivalent would be
The quickest alternative would likely be to use translation to squish all the white space first and then do regexes to strip the (perhaps) remaining single spaces at the beginning and end of the string:
(add extra whitespace equivalents in the translation if you want to lose carriage returns and such).
In any event, the point was that the join/split is an interesting alternative, and not all that inefficient. Lots of times when I want to strip extra whitespace speed isn't that big a deal, anyway :) Some people like to use s/^\s*|\s*$/g to strip leading and trailing whitespace but that's less efficient than doing two substitutions, so it's not always about speed.
Perhaps I can persuade japhy to present his benchmarks?