As I said above, I liked the sound of the M1s. They sound clear and are pretty warm, neutral headphones that don't overaccentuate the bass or treble. They don't deliver a ton of bass, which will probably disappoint bass lovers, but otherwise are pleasant headphones to listen to for long periods. They're well matched to a variety music types, though hip-hop isn't one of them.
What keeps the M1s from sounding truly excellent is that they aren't terribly open or "airy" headphones; the sound feels a little recessed (the soundstage just doesn't seem all that wide).
At around $120 online, I compared them with the $100 Noontec Zoro HD headphones, which are modeled after the Beats Solo but cost less and sound better. The Zoro HDs offer a little more dynamic and open sound than the M1s, but I found the Philips more comfortable to wear.
Another model I had on hand for comparison was the Jabra Revo headphones, which cost around $150 online. They're similar in terms of comfort to the Philips but offer more bass.
Used as a headset for phone calls, the M1 headphones performed fairly well. The microphone may be a little low for some people's tastes (you'll probably find yourself pulling it up closer to your mouth when you're making calls), but callers said I sounded OK, and I could hear them fine. Of course, your results will vary according to your environment and how much ambient noise there is.
The Philips M1 is a very likable headphone model for day-to-day use. They may not offer truly excellent sound for the money, but it's quite decent, and just as importantly, they're very comfortable for on-ear headphones; they're right there with the Bose OE2i headphones, which I consider among the most comfortable as on-ear pairs go.
Ideally, of course, you'd find a model that offers fantastic sound and great comfort for a good price. The Philips Fidelio M1 headphones don't quite get there, but as long as you aren't looking for big bass, they're a solid, versatile day-to-day pair.