I have been working on both the sales and the delivery side of our business, but not that many have had the chance to do so. I think more should.
One of the things I miss from my diminishing developer hours is the excitement of having a chance to do some new and interesting. The best of I was also a part of selling the solution to begin with.
Lately I have been mostly only involved in the sales side. There has been a couple of those really exciting projects I would have loved to also be part of implementing them.
As a manager I now see such cases as a great opportunity to offer such thrilling opportunities to others. And even if I don't get the chance to work on those problems there is the added satisfaction of others not only getting excited to have the opportunity to work on those interesting problems, but also seeing them grow and learn new things.