[angersock]

The codebase itself isn't the problem, really.

What happens is your engineering talent--if you have any to speak of--starts to get really pissed off that they've had to repeatedly cut corners and now are being expected to save the day. This causes lots of stress, and the more experienced the engineer the more likely they are to either ragequit or make large compensations demands. It's not that the cutting corners is what bothers them...it's that the other folks so badly misjudged the business that the cutting corners was ineffective.

Alternately, a competitor is able to look at your product, build a better architecture, and just plain kick your ass because it's more extensible and they can ship faster. I don't have any good examples for this offhand.

As nostrademons points out, though, you can get farther with a good sales team and a shit codebase than with no sales and a great codebase. Lots of examples of that (including my previous startup).