Planning an analytics-like system

[dhaktar]

The ProblemHi, I work for a company who has a really big e-commerce website with lots of daily visits, and I need to build a system to capture unique visits from people comming from sources like organic search engines (Google, Yahoo, Bing), affiliate programs and price comparison services (Google Shopping, Froogle). Moreover, it needs to track a visitor all the way from landing on the site to buying a product (thinking about Cookies), so that the marketing folks are able to understand the paths that are likely to result in the user placing an order (eg. when a user finds our site in Google Search and then clicks an ad in an affiliate site, he is probably going to order something).We also need to be able to track which visit is related to which order in our system, and besides that we have plans to add more reports and things that are not supported by Analytics (that's the reason Google Analytics does not suffice).How To Tackle The ProblemI know Google Analytics used images to do his thing in the past, and now it uses a JavaScript-based solution. And for some reason, Analytics is not very reliable, because it has big margin of error. I can imagine but can't know for sure why Google decided to change his approach from images to JavaScript, since some users don't enable JavaScript.So, knowing that our site and its resources are cached in a CDN, I'm considering two solutions:[*]Placing an image on the page that calls a Generic Handler (ashx) to process the visit, identifying where the user came from (organic search, affiliate, etc). The problem is that whe the handler executes, the URL referer points to my site's URL instead of the original source. I know it makes sense and all, but I need to be able to get the source that brought the user to me, and I don't know how to acomplish that without using JavaScript to modify the image SRC attribute to include a QueryString parameter telling me which is the actual referer.[*]Using JavaScript to make the call to some API that will register all the data I need. JavaScript will be able to get the correct referer, but I fear this solution because it will fail for JavaScript-disabled browsers.So, what are the pros and cons you consider about these solutions, what other solutions do you guys imagine, and what other general advice would you give on the matter?Thanks in advance!