I use old carpet under organic mulches extensively in my yard. Works great, better than landscape fabric IMHO. Some people (not me) do have concerns over chemicals in the carpet leaching out into the soil -- I don't know if this is a valid concern or not, something I think each person would have to judge for themselves.

But, from a cultural standpoint, it's a very good practice, keeps out weeds well. I haven't had any problems with water going through it once it gets soaked up/moistened. It's only first when it's dry (especially if its new carpet with the sort of waxy/plastic feeling to the back that is typical of new carpet) that it seems to repel water -- you can wet it down with soap and water or any surfactant to overcome that, but after a few weeks it happens on its own.

I use it too in between beds. It is the ONLY thing that will suppress weeds for me. Weed seeds that get into the air will root in a thick layer of mulch or gravel. I have no problems with water draining through the carpet. You can see mine in the link that I've provided.

Here is a link that might be useful: Carpet between garden beds

If you do not put mulch over it just make sure the pattern fits the decor.

hOT pInK and BOOGER YeLLOw look just plain gawdy!
So there!

I am in agreement with denninmi.
I have used old carpet for many year & my children Have one head,two eyes, one mouth. So it is finely safe, nothing has showed up in the soil test.

I have an artificial pond and stream and I used carpet as the underlayment. It sometimes sits in water with wet soil and it does not rot or stink. I don't know why I didn't think to use it for paths. you could move the paths around which is not so easy with other materials.

WOW! I saw this thread this morning and got so excited. I have a lot of 4x4 carpet squares from work, I was going to use them in my house but we tiled instead.

I was wondering what I was going to do with these carpets squares (not really wanting to haul them to the dump) - wondering how I was going to get rid of the weeds growing in the paths between my raised bed(wood chips are expensive). Thank you for resolving these two pressing problems (lol).

I use them extensively around my vege and yard, covered with wood chips. Even after a couple of years, if the weeds take hold in the wood chips, they are super easy to pull.
It seems like the outdoor carpet would last even longer than the indoor! You don't really need to water the paths anyway, so it shouldn't matter, right?
PS carpet scraps are usually free behind any carpet store. Just clean up after yourself. The less they have to take to the landfill! Nancy

nancyjane is right, but you should ask first and promise to straighten up after you pull stuff out. You want the store's dumpster to be neater and have more room afterwards. Sometimes that is not completely easy. You shouldn't leave a semi yanked out carpet taking up as much space as before you started.