I have yaktrax. They fit just fine on my running shoes. I have found that they feel odd in the beginning but you get used to them after a bit. However, there are some things you need to know -- first of all, if you put them on in your house, be very careful! On wood or ceramic floor you will wipe out big time! The wire may also scratch your floor, but the biggest hazard is falling.
You shouldn't wear them on the pavement as it will wreck them. I have heard of some people whose wire broke after only one or two times of wearing them, but don't know if this is because they were on the pavement. I have also heard that if you want to run in them, you should buy the Yaktrax "Pro" version, but I only have the regular ones. They won't damage your shoes at all.
So you are pretty well resticted to wearing them on the snow or ice. If it is a mixture of bare road and covered, then you have a problem, as you have to try and stay on the snowy/icy areas. I have worn them on the snow and they did collect snow some, but it is worth it if it is icy underneath. I have worn mine trail running which was interesting. Everything was good except for the time that I got a little wee twig caught in them, and I ended up being flung to the ground on my face. But that was only once.
So as you can see, there are pros and cons to them. Sandy says you can put screws in your runners and they will work. I have used my yaktrax several times in the freezing rain. We have a sloped driveway and it is NASTY getting up and down it in the freezing rain. Well, with my Yaktrax, it doesn't feel like it is icy really. Someone has told me that you can't wear them to run on shear ice, but they sure work REALLY well for walking on it. I love them for that. I got them for my parents for when they go walking too -- like I said before, the only problem is you reallly need totally snow covered or ice covered roads/sidewalks to use them. But they also slip off and on easily enough to, and fit really well into a pocket when you don't need them.
Oh, where can you buy them? They used to sell them at Soft Moc, but I don't know if they do now or not. They were $40. I got ours on E-bay and paid $20-something.
http://search.ebay.ca/search/search.dll?from=R40&satitle=yaktraxThey sell them at MEC -
http://www.mec.ca/Products/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524442541441&FOLDER%3C%3Efolder_id=2534374302733919&bmUID=1166401087609
