I'm one of the few (lucky?) ones that uses both KiCad (offical 4.0 released, yey!), as well as Altium 15 (at work).
Although I'm actually a SW guy, I can tell you that they both have their ups and downs, which isn't surprising when you're comparing products from the same segment. However, I can tell you that for prototyping work (just making a few one-off boards), I'm _much_ quicker in KiCad than any of our HW guys are at Altium, including the rented gray-beard that's been living and breathing Altium since dinosaurs ruled the earth.
And that's the entire chain, from building custom components+footprints to the finished PCB layout.
For cases like these (small production runs, single sourcing, etc), you'd be insane to pay for Altium. The time to learn KiCad is easily offset by the price of Altium licenses.
HOWEVER.. Where KiCad falls completely flat on its face is when you're planning for high-volume production. The BOM management is near non-existent, and good luck integrating into anything resembling a PLM system.
I guess this is kind of expected, as KiCad comes from hobbyists, tinkerers and academia (Go CERN!), none of which have probably been exposed to the added complexity of manufacturing (for example) 10K units a months for two years, and having to have the final unit produced behave identically to the first one.
And to show what level I'm roughly at, this is the latest design I did:
It's the latest take in my never-ending quest for the ultimate development-"buddy" when doing embedded software.
It contains:
* Dual JTAG, with a CPLD to do pin-routing and level-shifting. I.e, works with systems running anything between 1.0V and 3.6V
* Serial->USB converter
* Dual LM317 power-supplies (yes, I could do better with DC-DC bucks, but when I'm developing, 20mA is considered "high-current")
* Integrated current-monitoring/logging over USB (10bit ADC, 1KHz sample rate. Good enough to tell if I made things better or worse, power-wise)
* A small USB hub to tie everything together to one micro-USB port
From idea to second revision of the PCB layout (wasn't happy with the first one. Size and neatness of routing), this took about 10 hours. This includes building the custom components for a few minor chips, the 64-pin FT2232HL, as well as the 100-pin CPLD.