I use a fair amount of it. I'm using it to feed three of my four HF/MF antennas, one receive-only and two transmitting antennas.
The impedance mismatch you get when you mix in 75 ohm cable into a "50 ohm" system may or may not matter to your situation in a way that depends on a whole lot of details. The exact impedance of the antenna can pose problems. If you feed a dipole high above the ground you'll probably have it "just work." A high dipole is close to 70 ohms impedance, so a very good match to the 75 ohm cable. The worst case SWR referred to 50 ohms at the radio end of any length of 75 ohm cable feeding a 70 ohm antenna would be about 1.6:1.
But I had a big problem with a 40m ground plane antenna that was ~30 ohms. 30 ohms by itself is a 1.67:1 SWR and acceptable if you use 50 ohm cable.
But the *transformation * caused by 75 ohm cable could make the SWR at the radio end of the cable as high as 3.64:1.
I encountered this when I tried to feed my 40m ground plane with some coax I found, that turned out to be RG-11. I tried to tweak and tune out at the antenna and could never get it below 3:1 SWR.
The mismatches are never going to be severe enough to cause noticeable extra losses, but they can cause some issues with SWR... you can probably usually sort that out on a single band by changing the length of the 75 ohm line but sometimes that becomes impractical. Adding an extra quarter wave of coax to a 160m feedline is not the best solution, for example :-). The use of transformers can be helpful to transition in and out of 50 ohms in some cases.
There's a very simple transformer called a "twelfth wave transformer" that is just alternating sections of 75 ohm and 50 ohm coax:http://www.tuc.nrao.edu/~demerson/twelfth/twelfth.htm
I've built some of those using RG-6 and RG-58 or RG-8/X and they work well enough across a few ham bands.
You can also build ferrite broadband UNUN transformers. You can buy them too but that almost certainly defeats the cost savings of using the cheaper coax...
Here's a good resource:http://vk1od.net/transmissionline/RG6/index.htm
Anyway, that's a long story. The short one is yes, I use it, yes I use it on transmitting antennas, and yes it's worth a shot.