The key is to test the areas that you are most worried about going wrong. That way you get the most benefit for your testing effort. It is better to … - Martin Fowler

Often designers do complicated things that improve the capacity on a particular hardware platform when it might actually be cheaper to buy more hardware.

Graphical design notations have been with us for a while... their primary value is in communication and understanding. A good diagram can often help communicate ideas about design, particularly when you want to avoid a lot of details. Diagrams can also help you understand either a software system or a business process. As part of a team trying to figure out something, diagrams both help to understand and communicate that understanding throughout a team. Although they aren't, at least yet, a replacement for textual programming languages, they are a helpful assistant... Of these graphical notations, the UML's importance comes from its wide use and standardization within the OO development community.

Often you'll see the same three or four data items together in lots of places: fields in a couple of classes, parameters in many method signatures. Bunches of data that hang around together really ought to be made into their own objects.