That depends on which way they are comparing. Most of those comparisons I have read compare Bush's power grab, economic policies, and foreign policy to Hitler's, and those comparisons are right on the money.

If you take Hitler's first 6 years in power (1933-1938) and compare to Bush (2001-2006), you find lots of similarities. The Patriot Act is the Enabling Act almost word for word. Reichstag Fire -- 9/11 Attacks. Invasions of Czechoslovakia / Iraq - curcumstances very smiliar with both. Large government contracts to friendly corporations. Huge military buildup. Rubber stamp congress. Increasing power of executive branch. Executive branch no longer required to follow laws. Fighting "terrorism" given as main excuse for most of these things. etc, etc. Very similar.

However, if someone is comparing Bush and Hitler and brings up Jews/Muslims as the comparison, or anything to do with genocide or the holocaust, then they are out of line.