Literally means "Your mileage may vary" but is often used in forum talk meaning that your results will vary
Internet shorthand used to represent 'your mileage may vary' meaning 'how far you will be able to go depends on (usually external) factors relating to yourself', such as locality. Often used in deal forums to indicate that the OP (original poster) was able to complete the deal but it is unlikely or uncertain that others will be able to do the same. Can also be used to represent 'your market may vary' which is more appropriate for internet deal forums and more easily translates to some, especially people foreign to the english language. Often used in internet forums to indicate the likelyhood of something happening is uncertain.