If you've played around with Report Builder, you have probably used the Formula builder to modify an expression in your report or create a brand new field to display in a data region.
If any of the expressions that you build reference a field/attribute in your model, you've probably also noticed that you can't just type it (the field name) into the formula window and get it to resolve. You actually must use the Field List and add the field(s) in question. Unfortunately, we're not going to get "automatic" name resolution in 2005. So, get used to double-clicking your field names :)