For the HTML resume on this website, I tried to vertically align the content of the left column of tables to the top. The simplest way I figured to do this was to create a colgroup for the left columns and valign="top" in CSS.
But, it simply didn't do anything, even if I aligned directly on colgroup in the html. Ultimately, I just created one class applied to each cell that occurred in that column, and that class had valign set.
It worked fine, but it seemed strange that something so amply documented as valign for colgroups, simply doesn't work. I found the ultimate proof that it doesn't work on this w3 page, demonstrating valign in colgroups:
I only tried this on Mac, but it failed for me in FireFox 3.0 and Safari 3.2, though it worked in IE6 through Crossover.
I'm still looking into why.
I found a forum conversation from 2006, that says Firefox doesn't support colgroups.(Note: it's not a very civil back and forth, so they don't really get very deep into it, or agree that it doesn't work, though my sympathies are with the person who started the thread and her view that it doesn't work):
Two things are suprising, first that it applies to Safari as well(I haven't tested it on the current IE), and secondly that there hasn't been a change since that time..