So we had an interesting issue where sorting product by price was not working correctly for wp e-commerce products.
The sorting was happening but MySQL was sorting the wp-postmeta.meta_value as a string, so 12.95 was coming AFTER 123.
The solution is nice and simple
This way the MySQL does this:
was: ORDER BY wp_postmeta.meta_value
new: ORDER BY wp_postmeta.meta_value+0
Note the difference? The +0 forces MySQL to treat meta_value as a number and sort by that.
This tip comes from Tom @ http://www.tomandvez.com!