matt this is great! this was my initial concept of the use of creating custom grids... so that one didn't have to be "boxed in" to a preset. particularly in the case of ancients where getting unanimous agreement on what constitutes a full set of any given series means.
a second option that was never implemented, but could be if it was asked for, was to make custom grids available to other members so that if another collector liked your grid he could import it into his own account rather than have to recreate it.
i've heard little feedback overall on the grid feature and since they are not indexed by tantalus i have no idea whether it's a popular feature or not. with any luck, if tantalus continues to grow, people will gravitate to this innovative take on the penny books we all knew as kids.