We've done a lot of painting in the past few years -- we're by no means "experts", but we've learned a lot. Of course, the old adage holds true: prep work is 90% of the job -- something I learned the hard way when trying to skip wet-sanding when priming my first car for a re-spray (oh, to be sixteen again...).
Most recently, we've learned to make sure you invest in good product, choose that product wisely (the most expensive is not always the best choice) and be wary of label-claims.
Much of the body of the house is painted in Sherwin-Williams Duration paint (mixed to a Behr color: Squirrel). It's been a great choice for us. It's expensive at about $50/gallon, but it's been getting great pro-reviews and the exterior of the house is something I don't want to re-paint anytime soon. The guys at the local shop rally know their stuff and know their product beyond a simple PR pitch. Sherwin-Williams is also a bit further than the local big-box and they're not open as late... so, unfortunately, they're not the automatic fall-back.
Enter Behr paint. It's something that gets good reviews from homeowners, but not necessarily from pros (and who are you going to trust?). Behr has been a fine choice for the interior -- we've used the flat-enamel which has just a bit of sheen to it. It's a bit thin and the coverage/hideability could be better (especially in white), but it's available, and affordable. It's worked well an I'd actually recommend it for interior use -- especially with muted, mid-tone colors.
We've also used Behr's Ultra exterior paint (flat) for the exterior trim -- mixed to a custom gray-brown. Unfortunately, Home Depot switched their paint formulation method in the past 2 years, so the paint that we started with -- "beam brown" as we call it -- couldn't be mixed by the same numeric formulation that we had it mixed to a year previous (and when presented with the old numeric color code, the paint guy was a bit of an asshole -- oh, the joys of dealing with moderately paid and semi-skilled retail employees). So, our old beam brown is a bit darker than the new beam brown which means a lot of repainting for us. All that said, the exterior flat -- with a bit of Flotrol mixed in -- has a good flow, good coverage and a nice sheen when dry. I'd also recommend it, but suggest sticking with a simple non-custom formula and again, the mid-dark tones.
We tried Behr's Ultra semi-gloss for the door in a bright yellow hue -- the paint is advertised as "paint and primer in one". I hoisted our brand new exterior door on the sawhorses, gave it a good prep-sanding and laid down the first coat, waited for it to dry and applied the second. It had terrible coverage/hideability and after a few of the coat/wait/recoat steps, I began to look closely at the finish. Not only was it terribly orange-peeled (even with a foam roller), but it was nearly transparent and the paint just didn't seem like it was sticking. I gave it a tug and it all started to peel off. Four coats of paint and an entire day of painting peeled off in less than 5 minutes. Oddly, it balled up really well and I now have a tennis-ball-sized hunk of yellow paint which I'll likely send back to Behr (Home Depot gladly refunded the purchase price when presented with the ball of paint which was formerly on my front door). This all happened on a Sunday.
I booked it to S-W. On Sunday, they close at 4pm and it was 3:30pm already. I worked with Adrian who mixed up a color very close to the ideal yellow color. The Duration base was not formulated to support such a vibrant color, so we went with Resilience which has better drying characteristics (a good thing since we already lost most of the day). The paint went on wonderfully, had great coverage and dried quickly. We were able to get a base coat on the door and hang it so that we'd actually have some security that evening. While I'd have rather painted the door flat and hinge-less, it ended up working very well.
So, lesson learned... Behr: a good value when used for the right things. Sherwin-Williams: expensive, but worth it.