CAC Payback Period > LTV:CAC Ratio - Something I wrote a while back. LTV:CAC type ratios are useful to a certain point. The payback period is more imporant. The problem is that CAC only measures efficiency and not a good indicator of multiplying effects. Instead you need to look at acquisition vs retention vs expansion numbers.
12 essential product adoption metrics and how to calculate them - the usual suspects. archive
Dashboards
Read the original post for more details.