My mind, and the places it goes

i agree with you, in principle. i'm a roux purist, but i adore making it in the microwave. it's just so darn much faster. i draw the line at using roux from a jar. :) often, however, after microwaving the roux to near-doneness, i'll transfer it to a pan and finish it in the traditional way so that i can add my trinity. once the onions are translucent, i brown any sausage or uncooked meat/poultry that's going into the gumbo. if you don't use smoked sausage, you really want to add some smoked paprika to the soup to give it that rich flavor.

i agree with gilana that you can burn it, and you can also do it lighter by cooking for less time. for example, if you wanted a blonde roux to put in a bechamel sauce or something like that, you'd just shorted the initial cook time to 3 or 4 minutes.