particleman - 2:36 pm on Dec 8, 2012 (gmt 0)
I was in a similar situation as you. Google's conversion tracking is pretty easy to implement so I say do it. It allows you do all of these helpful features down the road if you want. I also tagged urls and kept my own data. This was important for me to validate conversions using direct data, not rely on google. In my experience the google data is pretty accurate, but on average I had a variation of around 1% comparing google's conversion data to mine.