Business Logic Layer

[Trinity]

I am programming data driven applications using asp.net with telerik controls (v2009 q2).I have a class named BLL which contains (almost only) static classes that return different objects taking some id as parameter. The generally return group of objects as Lists.My question is that are there any architrectural flaws to this, always using static. I know people make their Busines Layer and DataAccess layer as different projects. What is the advantage of it being a project ? So I can add more functionality or just it is tidier that way.Thanks in advance