<p>Is it "acceptable" to have an <strong>ASP.Net 2.0</strong> application without the BLL (Business Logic Layer) as the following?</p>

<ol>
<li>SQL Server Data Storage &amp; Stored Procedures</li>
<li>Data Link Layer (Strongly Typed Table Adapters) connecting to Stored Procs</li>
<li>Presentation Layer ASPX Pages with Code behind and ObjectDataSource for connection straight to the DLL</li>
</ol>

<p>Is a BLL always preferable, even if business logic is entirely validatable in the presentation's code behind?  What are the potential drawbacks for not using a BLL?</p>

Like everything else it is environmental and depends on the use of the system.  The question you need to ask your self is:
Will this be actively developed
Is this going to be used over the course of many years and expanded on
Is the expansion of the application unknown and thus infinite
Really it comes down to laziness.  How much time to do you want to spend reworking the system from the UI?  Because having no business layer means duplication of rules in your UI across possibility many many pages.
Then again if this is a proof of concept or short demo or class project.  Take the easy way out.