asp.net, ado.net, c# question

Jeff,
I like to break my design into three layers

1. Presentation
2. Business Logic
3. Database

1. In presentation layer I put only those that are of UI related. This will go directly into the aspx pages, user controls (usually I create on separate dll) and any UI related logic

2. Database. This is strictly database related classes. NO other code belongs here.

3. In business logic goes any middle-ware code that does not belong to any of the two categories.

Now, notice how I said 'This goes to separate dll' in the first case. I don't go crazy in creating many dlls. The rule of thumb I use is, if the code can be reused somewhere else, then I create it in its logical dll, so I can easily take it to another project and reused. That means the other layers may have multiple dlls as well.

Again, there are projects I have worked which they have only 2 layer or more than 3 layers. It does not have to be only 3 layers. The scope of the project will decide how you want to break your logical designs. In some cases you may be able to get away with single layer.