I appreciate any efforts a company makes in accomodating files from widely used applications like Photoshop, Illustrator and CorelDRAW. Still, I guess the primary benefit I see from an application like SignLab bundling in AlienSkin filters is those users who don't have Photoshop or another raster editor capable of using Photoshop plug-ins can use those filters.
There's still a lot of things Photoshop does outside of a set of add-on plug-in filters. The new CS2 version adds a lot of useful features for cloning objects in perspective, correcting barrel distortion from wide angle lenses, new high dynamic range image functions, more functions in 16-bit per channel mode, etc. In short, Photoshop is still my preferred raster image editor of choice and I don't see anything changing that anytime soon.
CAS applications have a great deal of benefits outside of what users normally have in standard desktop applications. The benefits are more clear in terms of vector based compositing.
For example, many people do like to design signs in Adobe Illustrator. I often use it (as well as Macromedia Freehand and CorelDRAW) as well. But Illustrator has this really punishing limit of a pasteboard far too small for large scale sign design. Corel and Canvas are the only desktop vector applications that allow one to design large signs at full size. But even Corel hits the wall at the 100' X 100' mark. I can go quite a bit larger in applications like Flexi. That can be pretty important when you have an entire building elevation to decorate.
IMHO, as far as raster image handling goes I think CAS-type applications will do enough to have dependable color control and good RIP functions. (It might be interesting to see how CAS-type apps and dedicated RIP apps like PosterShop Pro take to Adobe's new color control system in CS2 -it totally bypasses the system used by Windows). I don't see much need to duplicate much of the Photoshop toolset in the application. Again, this is just my opinion, I think such duplication leads to needless application bloat and sluggish performance. Lots of desktop graphics applications are guilty of this. For example, I see little need for Illustrator to include so many Photoshop functions. It's a vector drawing program, not Photoshop. I've been very annoyed by many of these applications wasting code on pseudo web page editing functions. I've got Flash, Fireworks and Dreamweaver already. I'm not going to use Illustrator by itself to design a website.
In general I would like to see graphics applications of all types concentrate on doing unique things no other application can do (and then do those unique things well) rather than water themselves down by copying features from other apps.