yes. it's incorrect, but not in the way some people might think. i have found (much to my chagrin) that supposably is an actual word...but, to my unrelenting joy, it is not what people think it is. confused? well, here are the definitions:
(click the images to make them larger and, therefore, legible, which is the whole point, right?)
[images snapped from m-w.com]
the problem is, most people who say supposably mean it as supposedly. as in, "he supposably had the 24-hour flu, which is why he called in sick yesterday." this misuse makes my skin crawl (which is actually the same reaction i have when i hear the word irregardless). in looking up the prickly word, my favorite discovery was this:
i felt such satisfaction when i found that. and, upon further investigation, i found that we are not the only people to blog about this.
[image snapped from languagerules.wordpress.com]
are you happy now, rachelle? :)