[schnoodleC]

ESSP is great because you are almost gauranteed that 15% return but the up side is much greater. I've made really huge money through ESSP plans. My strategy is:

1) Always invest the max, whatever it takes. It is soooo +EV
2) Unless there is a compelling reason be cautious about holding on to the shares. As an employee you already have lots invested in your company. Don't overinvest.
3) If the stock goes up a lot over the 6 months and you have a big paper gain then consider holding onto the stock for a year so that your profit will be taxed as long term capital gains rather than short term gains/ordinary income.