I just went into prod with a new Seam app.
What experience do you have regarding performance of Seam applications?
They seem to be very fast. Seam makes the connection of JSF and EJB simplier and does not seem to add overhead here.
Is there a way to cluster Seam applications?
Just as easy or hard as normal EJB apps I believe.
Does Seam use any proprietary, non-standard technologies?
Seam itself or at least a subset will probably become a standard (Web-Beans) one day but until then itself is not a standard. They also recommend Facelets (not a standard) instead of JSP (standard).