I've worked with a number of clients on SmartConnect from eOne Solutions this year as well as discussing with a few prospects. SmartConnect is a very flexible tool which can be used to integrate many different types of data. In this respect, it competes with the Microsoft Integration Manage product, but SmartConnect has many other features over Integration Manager.
Discussions on SmartConnect usually involve the question as to what data can be integrated by it into Dynamics GP; the short answer is if eConnect can do it then so can SmartConnect, but few people (including me) remember all of the nodes available within eConnect. As would be expected, this is also a common question direct to eOne, and one which Lorren Zemke addressed on the eOne blog: Tech Tuesday : What Data Can SmartConnect Integrate in Dynamics GP (eConnect).