Web Statics - What you want to know?

[Pogacha]

Hi, I'm finishing my sales web-site and I'm programing my php stats system.
I want to know what do you usually track? ( in addition to daily number of visits, sales and buys )

Thanks in advance.

[kay.altos]

visitor countries
visitor OS
referrers

(i think most of optionos of WebLog Expert)

[Pogacha]

Ok, thanks ...
My doubt is for tracking old visitors using cookies, is it helpful in any way?

By the way, the title must go " Web Statistics - What you want to know?". I'm very sorry ... I always check it before posting but it escaped me this time.