There would defiantly be more than a few failed CRJ Orals in this thread.

The only time single engine your going to have a fuel imbalance problem, is if auto x flow is inhibited or mel'd, while running single engine.

In which case single engine taxi will lead to a rapid imbalance, counter-intuitively dumping the excess fuel into the operating engines side (someone actually said it correctly than got called out as being incorrect).

The most likely scenario to get to an extreme imbalance, is to inhibit fuel cross flow on your before take off checklist (2engines), and then subsequently have your clearance cancelled go into a ground stop and go back to single engine forgetting to reselect auto x flow. It will happen fast and become quickly imbalanced.

Same thing can happen with the Mel if you don't heed the warning and decide to taxi out single engine with auto x flow disabled/mel'd, a rapid imbalance.

Other than that the auto cross flow works pretty well as long as its on.