Sometimes questions have no answers...
It can vary literally by 10x depending on the market, product, customer type.
Also it depends on your traffic source. Traffic from a good review? Should be high sign-up rate because they already understand you and are probably coming specifically to sign up. Traffic from adwords? Probably sucks. Traffic from StumbleUpon? A rate of 0.01% might be reasonable (no joke).
Obviously this depends on a whole lot of factors - what you're selling, how qualified the traffic is, quality of your landing page / web page, etc. etc. But in general terms, the benchmarks I've seen say that it's 1 - 3% for a paid service and 15 - 30% to sign up for free.
It will be interesting to see what others say.
Best of luck!