I started out by reading Matt Asay's take on the EUPL. And I read just about every article or post to which he linked. Asay says that the GPL, for better or worse, "leaks like a sieve." I can only conclude from his statement, "I really like the way it [EUPL] closes the ASP loophole without closing off everything else, as well" that Matt dislikes at least the ASP "loophole" in the GPL.
(Disclosure: As an employee of SourceForge.net, I am dependent on an ASP model, like Google's or Yahoo's, for my livelihood.)
But I'd fall into the camp which thinks the "leakiness" of the GPL is a positive rather than a negative. In fact, I think even the GPLv2 is a bit too strict for my liking. As I understand it, when you distribute (old-school) any software which you received under a GPLv2 license, you must license your own modifications under GPLv2. Emphasis added to stress this point - any mechanism that sets up a "you must _____" condition places an inhibition on the recipient, not a freedom.
Apparently, the HPL, EUPL, and GPLv3 take this same inhibition and make it even more invasive. Under these, when you "communicate" (new-school) any software which you received, you must license all of your own modifications under the same license. The "communicate" term is defined in every license (or an equivalent principle is established) to prevent a person or corporation from using such licensed software to distrubte services (SaaS) without releasing all their own modifications or enhancements to the software.
I'm fine with these kinds of licenses, I suppose. I just don't happen to share this kind of perspective - feeling betrayed or cheated if someone enhances my software but doesn't give their stuff back to me. IMO, their work and labor went into those enhancements so I'm fine with them licensing their stuff however they want. I rest easy knowing my stuff will always be LGPL and (theoretically) usable by anyone. I'll admit this a pretty individualistic perspective. But then isn't the open-source community just made up of individuals. Why do we need someone like the EU or FSF to tell us how to feel, or what's best for ourselves?
I think the majority of people in the open-source community don't mind that Google and Yahoo (and SourceForge) modify some open-source software but don't distribute all those modifications when they "communicate" that software via their SaaS websites. Combine that with the fact that some of these extra-invasively-viral(?) licenses prevent other business models besides just the ASP one, and I can't imagine these licenses will be very popular. (Indeed, GPLv3 has already been ranted upon by more than a couple open-source supporters.)