I've smoked pot since highschool (and know a lot of people who have done the same).
Sometimes I'll go months without smoking it at all...and other times I'll smoke 3-4 times one week. If it's not around I don't think about it....if it is around I often opt not to smoke it.
I am a very successful 27 year old with a condo, a great career, boyfriend, etc. and it doesn't effect my life in any negative way. I also have a chronic stomach condition and was told by my doctor that marijuana has been reported to help many people with my condition (although it's not yet a condition where marijuana can be prescribed) so when I have a bad stomach flare up I sometimes smoke and it eases the pain.
My bestfriend is a lawyer and smokes pot just about everyday. She has a great job, also owns a condo, has a wonderful husband and lives a very happy productive life.
That said, I do know people who smoke everyday all day long and their lives seem to have gone nowhere because of it. I don't know why it effects some people differently than others. I can only speak for myself when I say that I use it both recreationally and medicinally and have never had a problem.