There is a problem with the Buy Button IDs on a category page.
First, they all come out looking like this: <input type="submit" name="tcp_add_to_shopping_cart" id="tcp_add_row" value="Add"/>
So all the buttons on the page (several if listing a category) have the same ID. That won’t validate, and there is no class specified, so it makes it hard to apply styles.
The options for the price have the same problem. <select name="tcp_option_id" id="tcp_option_id">
And even the hidden ones have the same ids <input type="hidden" name="tcp_option_1_id" id="tcp_option_1_id"/>
Not as severe, but still a hassle: the first row of the Buy Button table has the headers for Price and Units, but there is no class on anything in that row or cell, so I can’t style it.