Overtly advertising it? No. Hasn't stopped me (and quite a few others) from getting 4 day weeks out of them.

The trick is being senior enough (or in demand enough) that you can get one company to agree to a 32h week for you (and be willing to walk - I've interviewed with very interesting companies who weren't willing to consider it, and so we ended the discussions).

Once you have it in some form or another, you're good. It's just a condition of employing you, early in discussions with other companies.