This is funny. I work in the office. I would estimate 75% of the offices are empty, even in the groups like development. Everyone is working from home so they say. Basically, this is the unwritten code that you will probably wake up and send off a couple of emails, and you will answer a few as well. I highly doubt that more than 10% of the folks are actually working on any Friday. I know a lot of folks claiming to work 60+ hours/day. These people are full of it as they have the time to "work from home" on Friday. Email volume could be tracked for a Friday, and the metrics would likely show a 50% reduction in email.
We do offer summer fridays, but we also offer spring, fall and winter fridays as well. HR would be happy to talk to you about this any day of the week, except Fridays, when they are working from home as well, and conference calls on Friday after noon are just plain wrong.