Posing QU's on Google Variables "aclk", "gclid" "cd", "/aclk" "/search", "/url" etc

[James77]

I've been doing a bit of stats research prompted by read the recent ranking blog http://www.seomoz.org/blog/gettings-rankings-into-ga-using-custom-variables

There are a few things that have come up in my research that I'd like to clear up. The below analysis has been done on my "conversions".

1/. What does "/aclk" mean in the Referrer URL? I have noticed a strong correlation between this and "gclid" in the landing page variable. Does it mean "ad click" ??

Although they seem to "closely" correlate they don't exactly, so when I have /aclk in the referrer Url MOSTLY I have gclid in the landing page URL. BUT not always, and the same applies vice versa. It's pretty vital that I know what is the best way to monitor adwords PPC, so what is the best variable to go on? - Currently I am using "gclid", but I have about 25% extra referral URL's with /aclk in that dont have "gclid" in - so am I underestimating my number of PPC conversions?

2/. The use of the variable "cd" is great, but it is not always present. I have noticed that 99% of my google "Referrer URL's" either start with:
/aclk   - No cd value
/search - No cd value
/url - Always contains the cd variable.

What do I make of this??

Thanks for the help in advance!