I purchased the Sennheiser Adidas Earbuds model CX680 hoping to get a decent pair of headphones for walking/jogging. I had a few concerns I originally wanted to solve, and a few more I've learned about since trying these earbuds out. My biggest concerns are:

• Keeping them in place! I sweat a lot, and it is super annoying to have earphones that slip out of place.
• Non-intrusive cable. I really dislike dangly things weighing down such that it pulls on the earphones or just plain gets in the way.
• Relatively non-obtrusive to wear. I don't want a headband or even wraparound earphones if I can help it. This goes hand-in-hand with the sweating, and I don't want to have to work around the devices. Something limited to just the ear area is really what I want.
• I've never had real earbuds before, so I wanted to try them out.
• Decent sound quality. Hey, I do have my standards!

So here are my pros and cons on the CX680.

PROS

• The cable on the CX 680 is awesome. Not only does it detach in the middle, shedding the excess length and the weighty volume control leaving it a perfect length for connecting to an arm-mounted device, but it's lightweight, doesn't tangle, doesn't catch and drag on my skin or clothes. Absolutely loved the cable on these things, even despite the very bold lime neon color.
• The sound. I doubt I'll ever complain about sound quality with Sennheiser products (I'm a fan), and I certainly have no complaints about sound fidelity on the CX680. The sound is rich and the bass (which I tweak up a bit on my mp3 player) comes through like a champ.
• They stay in place, as long as you keep them in place.
• Noise cancelling. These earbuds certainly do cancel out ambient and nearby noise. But then again, so do probably most earbuds by nature. Might be useful in a gym that plays awful music or someplace where you have no need to hear anything else, such as a long airplane trip.
• The flexible earfin design is actually really neat. I truly expected these to fall out immediately, but once I moved up to the largest included earfin size, they slipped in easily and beautifully. The earfin also makes these earphones that easiest pair I have to tell left from right (the earfin points forward).

CONS

• Earbuds. Yeah, I got this hoping to try out the earbud idea, but I find there are some very real drawbacks to having earbuds which seal in tight to your ear. First, I could immediately and loudly hear the wind whistling across my ear. Second, I couldn't much hear anything else. Some people will love the noise-cancelling effect and in some situations I would as well, but I almost universally prefer to still be aware of surrounding noises, so this is way too much cancelling for me. Third, I can hear myself swallow, breathe, and talk, just like when you plug your ears with your fingers. Again, all of this is because of the tighter seal that earbuds bring. I also don't tend to listen to my earphones at a ridiculously loud level; I'm a bit sensitive to longterm ear damage, so it's not like I need to hear my music crystal clear.
• Once you get your ear sweaty and slip these out and back in, you're pretty much expecting them to slip loose again at some point. While not nearly at all as bad as other earphones I've owned, I am still hoping to find a pair that just plain stay in place no matter what. To be more clear, the earfin piece was just fine, but the earbud part definitely felt less secure in the ear, though they never did actually fall back out in my use. I just found myself slightly distracted by them.

I love the cable on these and the sound quality, but unfortunately the earbud nature is going to cause me to try the MX680 next. And if I had to give an example of an earphone that used to stay put no matter what, I have these ~1998 Panasonic over-the-ear earphones that have a clunky slide-adjustable arm to go around the ear. I still have them, but they are markedly worse sound quality than any Sennheisers I own and look extremely chunky by today's standards.