Those wanting to knock Luther might want to note also his questionable role in the German Peasants War. Those wanting to do the opposite might consider his cultural contributions, which were considerable.
http://www.youtube.com/watch?v=YXzubuENjHkIn all seriousness, Al's made a bunch of good points in a row.
I do wonder, as far as his HP status, if we're bit unfair calling him a HP using a more modern or totally present day standard (yes, by today's standards he's got some really horrible aspects to him)...I really wonder if any person in more distant history would be a FF under such a standard...the contra position to that, judging him by the standards of his time might be too much in the other direction (ie, he was better, maybe, than the other folks of his era). Too lenient? Too easy to excuse bad actions in a contest of who has the least dirty hands. I don't know.