Two cable questions

1) Why does skin effect occur if electricity always takes the path of least resistance? 2) Is silver a better conductor than copper with both AC and DC, or just one?
Silver conducts 106%, if copper conducts 100%, and whether the current alternates or not, should have no bearing. I believe that there is less resistance at the surface of conductors, so the electrons are taking the path of least resistance, and hence the skin effect. It's more complex than all that, but I'm no theoretician. And just knowing the basics doesn't mean at all that you'll be able to predict which cables will work best in your system before you try them, either.
One thing to remember regarding the silver versus copper conductivity debate. Silver oxide is conductive, copper oxide is not. Thus, as these conductors age, the disparity between them becomes greater. Silver is best(AC or DC), followed closely by copper, then a fair sized dropoff to gold.
This is to quantify the conductivity differences of silver and copper. Silver: 62.9, Copper: 60.7, Gold, 48.8. So, silver is actually 3.62% more conductive. Source is MIT's website.
These are all excellent responses, but as Carl says, you cannot judge a cable by the specifications, whether you are discussing the metals, the insulation or the shield. Even micro changes in any one of these affect the final product. I have even tested soldering the connectors with three different types of solder, and gotten a substantial change in sound. Again, as stated over and over by MANY of the Audiogon posters, you need to try the cable in your own system, and not worry about who else likes it, or why it should or should not work.
I have tried the DIY CAT 5 recipe on with great results. Cat 5 network cable is 24 gauge Teflon coated solid core copper (99.99% OFC). Anyone else tried this?
You can buy 99.999% pure, teflon coated, 22 gauge solid core silver wire VERY cheaply(even cheaper for 50+ feet, $1.80/foot) at HomeGrown Audio. I will be using their version of Kimber KCAG interconnect. Only 2 differences: Kimber is stranded, this is solid core. The other difference, price 1 meter for $70(terminated)! I have used the KImber wire with great results, this may be even better.
Sol322, the three solders I tried were the Wonder solder, WBT solder and the custom solder manufactured for Purist Audio Design (do not know who made it for Jim). The WBT was the brightest, the Wonder Solder in the middle and the Purist was the most neutral. I tried these solders on interconnect cables, AC connectors (Hubbell), and on phono cartridge clips (that connect to a phono cartridge). If you need to buy one of these on the open market, the Wonder Solder is the most likely candidate. The Purist Audio solder I tested does not sell as an individual product, I got the sample from Purist in order to repair an interconnect that was damaged in shipping. Hope this helps!