I am going to be short here. I do not want to get into holy wars on which naming convention is the best. I just want to stress that it is very important that you have a naming convention. It will help you a lot. It will prevent many errors. It will shorten your development times. With a constant convention, you will be able to use different query builders efficiently, as most of them make joins automatically based on the same names. In DMX, for example, you can use natural prediction join, i.e. prediction join done automatically on same attribute names.
BTW, if this is so important, why does then BIDS automatically add spaces between words in names in an AS project? I do not know, and I hate it. As I do more with code than with GUI tools, this is something that makes me nervous. However, I have just learned something: with Excel 2007, you can create data mining models without this user-super-friendly feature. Oh, you probably noticed: this paragraph has nothing to do with naming conventions, this is grumbling. I admit, but I feel better now as well.