Step one: Paint with a roller
Step two: Continue painting with a roller right up over the edge of the trim for a small section--about 2 feet maybe (I've used just this mini roller to paint the entire living room...it has just never seemed worth the trouble to get out the big roller and pan).
Step 3: Grab one of these (every painter should have these...they're the best!).
Use the baby wipe to clean the paint off the trim quickly before it dries. Be careful (at least on your second coat) not to touch the wet wall paint with the wipe...but if you do, you can always fix it.
It works on the baseboards too. Yes, that is door and window casing that they used for baseboards. We also have that stuff along our fireplace weirdo-mantle and the top of the half wall.. It looks strange. I long to one day have real baseboards and trim.
Of course, I still use my handy wonderful angled brush for along the ceilings and areas like these:
When you're painting a room with four windows, two doors, and several random areas of trim, you have to take short cuts. So this is just one of mine.