I switch lenses all the time on my dslr, my prime lenses are so much higher quality than my zooms (for comparable prices), that I tend to use the primes the most.

HOwever, you do run the risk of dust on your sensor everytime you change, I've heard people say never ever change the lens on a dslr - but I guess those are ones who've gotten some dust that they can't get rid of.

THe leica lens on my fz20k was 12x and maintained f3 or something like that across the range of the zoom, which was just awesome.