Well, my book on Portlet Programming deals with JSR168, which is the basic environment for developing portlets. It also deals with the Struts portlet and the JSF portlet development. Of course, 6.1 provides all sorts of extra features, and I believe a JSR286 feature-pack, so you need to do your own digging on that.
IBM usually releases redbooks like crazy, which aren't usually all that fun to read, but they usually have a good deal of information. Plus, you can download them right from IBM, so maybe you could search IBM's redbook sites, and let us know if you find anything decent. I'm always looking for a book that reveals the latest WebSphere Portal development tips and tricks.
Oh, my signature links have some tutorials on portlet development with IBM tools, if you're interested.
Joined: Jul 28, 2009
Cameron, thanks a lot for your quick response. I am particularly looking for WPS6.1 book. I have looked out for Redbook, but believe IBM still does not have that out there.