I've been using a Sure Electronics ISP programmer and also my STK500 for ISP programming and I've never really given any consideration to ISP cable length. The one coming off my Sure model is 2 feet and I routinely add another 1-2 feet to it. I've never had an issue programming even up to at 1.8mhz or so.
I'm thinking about getting a dragon, but I keep reading how sensitive it is to ISP cable length. Why would it be so much more than the sure or stk500?
I admit to not needing a long length, but it can be flexible..