I believe that the only thing that matters is whether a source buys or not - how much traffic or subscribers I get from a source doesn't matter to me- all I want to know is , does a particular source buy from me or not$%:
I also believe in keeping costs low, and since I already $60 per month on web hosting, autoresponders and another tool, I just don't want to spend anything more up front right now - even though I made $3800 online last month, I think that the cost side is still important.
So the way I do it is, using aweber autoresponders, is create a different autoresponder tracking account for each source of traffic, create a duplicate web page for each source, and then keep on file with each subscribers' information, their original source. Then I take my sales and correlate their origins with the sale - and I just create a percentage of sales from each source, compare that to the percentage of money or time I spend on that source, and make decisions about the future based on that.
Certain samples
DK Concise Atlas of World DK CONCISE ATLAS OF WORLD HardcoverThe 2009 Import and Export Market for Copper Tubes and Pipes inNew Takes in Film-PhilosophyThe Modern Theologians ReaderBiddle, Stuart J. H. Mutrie, Nanette's Psychology of Physical
Another note, as long as you have randomly distributed sales, you can do the statistics on as few as 30 sales, as long as you randomly choose the sales you track, rather than use all the sales of the month, and the percentages will be within a few percentage points of the true number...
This allows me to save a lot of time and money on tracking, just by setting things up with the autoresponder tracking accounts in the first place.