Search Facet Numbers

Note: This is a follow up to a previously posted question.

I am working on re-implementing search functionality on a site for which search is quite important. There are tens of thousands of products, so faceting is a big part of how users search. There are dozens of properties that don't all apply at once. My question is regarding the best practices for showing the numbers next to facets.

In some search interfaces, you'll see a number beside the search facets:

Amazon and others, however, no longer shows these numbers.

I'm trying to figure out the best way to handle this. On the one hand, I understand that it may be of interest to users. However, I'm having a hard time making the numbers indicate anything useful when it comes to the actual data.

Consider my example above. If the user selects "Red", I would expect the numbers in the "Color" facet to remain the same, because if I were to check one of the other options, it would add to the number of results.

But if I checked "Red", what should happen with the numbers in the "Size" facet? Should they change to reflect the number of results that also are "Red"?

I have seen both options and more, depending on the implementation. Given that there doesn't appear to be a standard, it seems to me that the numbers are pretty useless.

Do I need to show numbers beside the facet values? How can I make them meaningful?