Classify future performance of customer
I'm not sure it will matter very much whether you have one row per user or if you have one row for per month per user. The important part is that the data you have is accurate for that user for a particular month. You might construct your training data like this:

--------|-----------------|--------------------|
cust. id| time on website | profit over 10,000?|
--------|-----------------|--------------------|
 3         30               0
--------|-----------------|--------------------|
 3         80               1
--------|-----------------|--------------------|
 5         100              1
--------|-----------------|--------------------|
 7         5                0
--------|-----------------|--------------------|


The important thing to notice is that even though customer 3 is in the dataset more than once, he/she has different values for their data features on which to predict, and different from how they were represented in the previous month. This is assuming that you are aggregating the data by month per customer.

This blog predicts customer churn, but you might be able to use the general strategy for your problem.