<p>What would the differences be in implementing remote business logic?</p>

<p>Currently we are planning on using <a href="http://en.wikipedia.org/wiki/Oracle_Application_Development_Framework" rel="nofollow noreferrer">ADF</a> to develop front-end web applications (moving from <a href="http://en.wikipedia.org/wiki/Apache_Struts" rel="nofollow noreferrer">Struts</a>). What are the differences between the front end calling <a href="http://en.wikipedia.org/wiki/Enterprise_JavaBean" rel="nofollow noreferrer">EJBs</a> using <a href="http://en.wikipedia.org/wiki/TopLink" rel="nofollow noreferrer">TopLink</a> vs ADF Business Components through <a href="http://en.wikipedia.org/wiki/Java_remote_method_invocation" rel="nofollow noreferrer">RMI</a> in terms of scalability as the migration from Struts to ADF will also encompass PL/SQL and Oracle Forms, thus increasing the user count drastically?</p>

I'm going through a similar situation right now. I'm am not an expert, but here what I've gathered from my experience. Whether EJB's using Toplink or ADF scales better depends quite a bit on the particulars of your situation. In some cases one might be better than the other, but I get the feeling that they are both pretty good solutions.
However since you mention that the project also involves the migration of Oracle Forms, then it seems that ADF would be the best choice since Oracle seems to be positioning JDeveloper and ADF as the successor for Forms and Reports (see the
ADF Documentation targeting Forms and Designer Developers
).