Whenever a new version of Photoshop Elements is introduced, current users of a previous version must decide whether or not to upgrade to the latest version. Often the answer comes down to whether or not the new features added in the latest version are capabilities that could be useful to the individual. In September, I posted a chart that compares features for PSE 6 through PSE 8. It is not totally complete, but does cover the most import features in my opinion. Here is the link to that earlier post.
In general, I recommend that if someone is still using PSE 4 or an earlier version, it is probably time to upgrade. However, deciding to upgrade from PSE 5 may not be that automatic. For example, PSE 6 was the first version that introduced the dark background. Many people found this hard to read. Adobe has continued their attempts to improve the readability in more recent versions, but it is a work in progress.
Another reason to upgrade to the latest version is the hope that whatever bugs/problems that existed in earlier versions have been corrected. That is not always the case. And of course, there are times when new problems are introduced in the latest version. That is the nature of software development. But generally speaking, problems in earlier versions are often, if not always, addressed and corrected. And of course, if you do not use a certain feature or capability of the the program that has a bug or problem, then its presence is not that relevant to you.