I'll put in my opinion that it is Adobe's responsibility. This forum is not indicative of the general user base. I'd be curious how many bug reports Adobe has received from people who never come to this forum, or how many complaints people have made to the retailers where they bought the programs.
Adobe has a huge variety of users, from students, hobbyists and dabblers, to seasoned pros. Many people will buy the Web Premium suite, for example, because they are Dreamweaver or Flash users, but need Photoshop as a peripheral program for creating graphics. These are not power users. And when they experience the performance problems, they probably shrug and think that Photoshop simply sucks by default and thank God they don't need to use it often.
Video card drivers may be faulty, hardware may be slightly different in individual systems, but the general consensus among those reporting the problem (including me) is that these performance problems didn't exist in CS3 and earlier, using the same equipment. The code should be robust enough, and generic enough, to handle all current hardware and CURRENT drivers. I'll add that other graphics programs I use which have OpenGL options, do not experience any lag.
I frankly resent some of the smug comments from hardcore users here on this forum, the ones not experiencing problems, using terms like "whining" and implying that those of us who are disappointed with CS4 just don't have it together technically. Screw you. I eagerly bought the CS4 upgrade the moment it came out. I own a video card on Adobe's "approved" list. I have a clean system. I experienced significant problems with Photoshop. Some of the workarounds have helped me achieve mediocre rather than poor performance; an improvement, but still hugely disappointing. And if I complain, I'm whining?
I definitely don't blame Adobe engineers and programmers. It's clear that Adam and Chris are the tip of the iceberg of programmers trying to set things right. And I'm sure no one in the development team would have allowed this version to be released if they'd been aware of the GPU problem earlier. But management obviously rushed the entire CS4 suite release prematurely to meet a sales deadline (it ain't just Photoshop: Flash CS4 is so extremely buggy I wouldn't even rate it as beta). It was also a management decision to limit the Photoshop beta testers to a set group, all of whom are likely super-advanced users with high-end hardware. Same with Flash (that I know for sure, since I know some of the beta testers). As a result, huge numbers of bugs go undetected because this user group doesn't access those functions as part of their work.
Adobe placed Dreamweaver CS4 for public beta, by contrast. I tried it, it was a real MESS. But they got a large volume of feedback from every type of user, and the release version is, so far, pretty tight. Makes a big difference when you let more than just your friends noodle around and find bugs that the power users might not discover.
They certainly would have heard of this GPU issue months ago if they had a less exclusive beta tester list. And at this point I think it's Adobe's sole responsibility to engineer a solution. I believe that they are working on it. The anger in this post is directed to the "I'm all right Jack" forum regulars who are so bemused by people like me.