This is like a marketer suggesting an engineer roll his own security. If its a fun side project, do it! If you actually want it to work, don't do it. If you want to /really/ use it (checking more than sessions), don't do it.
I don't think rolling your own auth or encryption is an apples to apples comparison.
One of the new hotness in marketing is micro-funnels. You have to have customized metrics built into the product for that to work.