I've done some short sleeves that look fine (see above), but as you can see, they fan out a bit. That means that they don't work as extended long sleeves. They result in a comfortable yet baggy and unflattering sleeve appropriate only for cave dwellers.
I've been sweating it out with my long sleeve pattern for a long time now--I started on my vacation last September, fiddled w/ it some more in January, then said AHGHGHGHG I can't do this anymore and set my sights back to sleeveless summer designs.
Plus don't you just love the awesome brown floral I'm using for muslin? It is a sheet set I got at Salvation Army--hence why I'm not using it to make anything for sale. Please excuse my looking like an ancient troll that just climbed out from under a dirty rock. It's Sunday morning after all.
To those struggling to make a sleeve sloper or modify a commercial pattern, I wish I could offer hard and fast advice. Unfortunately what you'll need to do is entirely contingent on the shape of the wearer's arm and torso. I found The Perfect Fit and Fit for Real People quite helpful. Sewing books and even pattern drafting books don't offer much in the way of alteration except in a pretty basic sense.