That's what most p2p guides recommend, for example:
http://dev.deluge-torrent.org/wiki/UserGuide/BandwidthTweakinghttp://www.makeuseof.com/tag/10-ways-to-speed-up-torrent-downloads/Personally, I set my upload limit at 75%: "240.0 kilobytes * 0.75 = 180.0 kilobytes".
NOTE: 240KB/s is my real max, even though my connection is rated at 256KB/s. The missing 16KB/s is TCP overhead, google it.
So if you use a guide I recommend you use your real maximum upload speed to calculate it, not what your ISP claims to offer.
I found that best since I share my upload bandwidth with 3 other computers.
Doing this I can download at my max of 1,800KB/s and upload at 180KB/s at the same time.
Just so happens to be 10%.
And even more important, while doing so I and the other three computers can still browser the web, check email etc, with no lag what so ever. Since there is still around 60KB/s of upload bandwidth to go around.
But at night or when the other computers are offline I use 100% of upload, so I get that nice 60KB/s boost. Which is crazy too, because just a year ago 60KB/s was my max. So triple the speed normally, or 4 times the speed at night. he-he