I noticed over at Centsational Girl that there were some questions about the rug tutorial. I bought the rug from Target, and it is made of synthetic materials. RIT dye specifies that it can be used on cotton, rayon, ramie, and linen blends. It doesn't recommend it for polyester or acrylic, but as you can see from my rug I did have any problem with the dying process.
If you're looking for plain rug remnants and want a higher quality rug I suggest calling local rug dealers about any remnants they have and what they're willing to sell them for. These are large pieces of rugs that are left over from custom projects that wont be easy for them to sell, so there might be some bargaining room. Most of these places will also bind the remnant for you, charging per every two feet. If you're nervous about how the rug will take to the dye I suggest getting a small sample from a dealer and trying it out on that first.
Surprisingly, the dye didn't leak under the tape. Either the rug absorbed it too fast for it to leak, or because I blotted as soon as I sprayed. There were only a couple of places where some over spray got on the white part of the rug. I "erased" these with some very diluted bleach. After that I was more careful to cover all the surrounding areas with rags. I hope this answers any questions. Happy dying!