In Eclipse (Europa Winter), I upgraded a project on which I last worked in 2006. It was a WTP project, and after a few small issues I had to fix, I was annoyed with many error messages concerning my TLDs:
"Cannot find the tag library descriptor for xyz"
My solution was to create a new project, with a WTP facet upgraded to the latest version. I had my web contents under the "web" folder, instead of the default "WebContent", and my theory is that the previous version (2.4) didn't work fine with non-standard directories. With the current 2.5, it worked fine and I got rid of all errors.