On the other hand, I'm a software engineer who is able to keep a clear separation between work and personal life, and I would very much appreciate the ability to spend fewer hours on work.
Though as others have suggested, a 3 month vacation every year might be an even better approach to a 75% work schedule.
And you wouldn't worry about people plotting on either how to get you fired, or I suppose in the "best" situation loosing out on working on the good/funner projects? From what I've seen from other people taking extended time off from work, it is super dangerous. Hell, I took three extra days for Thanksgiving and found myself removed from an interesting project and placed on some maintenance tasks afterwards.
Though as others have suggested, a 3 month vacation every year might be an even better approach to a 75% work schedule.