I watched today's announcement of Adobe's Creative Suite 4 online, and frankly, Apple can announce nothing better than Adobe (or most companies) can make a "big" announcement. From the very beginning, Adobe was on the defensive, with managers saying that "this is much more than a point upgrade." From what I saw, the need to upgrade depends almost entirely on whether or not you have to have the new features in the products that you use most. For some people, an upgrade is almost mandatory: Premiere Pro, for example, now supports both Red and AVCHD formats. If you need to edit video in either of those formats, it clearly makes sense to upgrade. On the other hand, if you're perfectly comfortable with what you can do with Illustrator or Photoshop right now, you might want to spend your money on other things.
This may be the point at which Adobe users decide to upgrade individual applications, rather than an entire suite. I've loyally gone from individual apps to Creative Suite to CS2 to CS3 over the years, but the apps that I use the most are Acrobat and Dreamweaver, with Illustrator following behind and Photoshop even further back. All of them work fine for me. I've been testing Dreamweaver CS4 for some time, but I can jump back to CS3 if I have to.
If you haven't bought into the Adobe platform at all, a suite may very well make sense, if you're going to use two or more applications. I believe, however, that there's not all that many creative professionals that haven't already bought into Adobe. Students can buy in at greatly reduced prices. And no, this announcement isn't going to cause a mad dash to Microsoft's creative applications, although some people might take the money that they'd spend to upgrade their Adobe apps and buy Expression Studio ($699 list for five applications).
Rather than purchase an upgrade as a knee-jerk reaction, check out the new features in the Adobe applications carefully. In this tight economy, you might do better to save your money and wait for CS5.