i have a 155... its my park/fun board. my regular all mountain is a 161. i'm 185lbs. but totally depends on how and what you are riding. i like the longer ones for speed and edge control. shorter one is great in the trees to hop around and hit the park.
i find everyone suggests things based on what they want. the guy who suggested 155 is probably a pure park rider and has a 150 with a super tight stance... doesn't mean its right for you... or wrong for that matter! people will tell you that the wrong size can ruin the sport for you... for me, nah. it would just make it a bit harder.
again, first board, i'd usually suggest smaller as well. and for your next one that you ordered.. should be just about right based on the weight lost!
if their are demo days, try out a few different sizes and setups. i love doing that.
you're exactly right. The guy in the shop rides pure park. Since i spent all that money on a new board it will definitely be motivation to keep losing the weight so i can ride this winter!
Thanks for all the advice.