I do but I can't give you the exact figures, that's not my decision to make.
The big problem is probably defining what people call 'conversion rate', typically that's 'virgin traffic' divided by actual sales.
The problem with that particular definition is to track accurately how many people have never seen your site before.
For a site that is growing steadily the number of 'new' visitors that will eventually convert over the life cycle of their account is a number that always relates all of todays 'new' traffic to the total sales of today, but the sales of today were not typically caused just by people that visited today for the first time.
So accurately tracking conversion rate is not as simple as it may seem at first glance.
Also, and this is a completely different issue, conversion rate is not the most important figure at all, and I find the thread we're discussing this in amusing because even though the first poster in the thread accurately identifies recurring billing as an excellent revenue driver it completely misses out on the life-cycle aspect of an account, and typically accounts do not last forever.
Industry standard is 3 months, so if your subscription site has a 1% conversion of free traffic to paying members then you will still only make 3 times your monthly charge on them.
To do better than that you'd have to work really hard on tweaking that 3 month figure, retention is almost as important (if not more important) as initial sign-ups.
That's where the real money is.