No necessarily. While I prefer using switch/case as well since I think it makes the code more readable, I have found that if/then's generate smaller code at least when using avr-gcc. At least this was the case (no pun intended) a while back. I'll need to double check the latest GCC version to see if it performs similarly.
I discovered this while doing some work on an AT90S2313 a while back which has only 2K of flash. The code was getting very tight and I was able to free up a significant amount of space by rewriting switch/case as if/then.
I'm still waiting on my copy, though. Amazon says it shipped today.
-Brian
-- Brian Dean, snipped-for-privacy@bdmicro.com BDMICRO - Maker of the MAVRIC ATmega128 Dev Board