I bought a pair of these a couple weeks back, and have tried them out on several runs now.
I have to say that once you select the correct size covers (included), they are comfortable, and have stayed in very well. There have been times when they feel loose, but that seems to be by their nature and doesn't necessarily mean they're going to fall out. In fact when I fell down running this morning they didn't fall out at all. They also survived a two hour run last weekend, only removed when I did so on purpose.
They do fit in a way such that you can hear more of what's going on around you than the standard inside the ear bud. Has turned a couple of what would have been "oops" skid to a halt or jump into nothings already. BUT, just a word of caution to those crazy audiophiles out there who expect Bose quality sound at all times, the extra room to let the outside noise in also lets wind rip through on breezier days. Stating the obvious I know: the more air that's in there the more interference and less volume.
We'll have to see about the durability, but as was said above I figured at $8 / pair why not take a shot. If this continues I might buy a backup second while they're on sale. I also had a good experience with the normal ear buds that were on sale a long while ago, and those have lasted, so who knows.