I apparently based my post below on incorrect information and assumptions that I made.
Per Imagenomic's David McDonell:
Imagenomic is working on and will be releasing plugin updates for CS5, and these will likely be provided FREE for registered users.
My apologies to the team at Imagenomic and any concern I might have caused other loyal users of their products.
Those of you who have upgraded to Photoshop CS5 already and are fans of Imagenomic's top quality filters (as I am) will be frustrated to know that they will not be supporting the existing versions of their tools in CS5. Noiseware, Portraiture, and RealGrain users might be able to get the tools to work, but on first attempt they would not install in the new CS5.
Imagenomic is working on updates to the tools but these are version upgrades which are not normally slated for free upgrade.
While the new versions will have better features, it seems silly that the old version wouldn't just work or be quickly modified to fit the plug-in format of CS5. Let the features of the new versions sell themselves. Don't hold the customers hostage to buying a new version just to have existing functionality.
UPDATE: I did manage to get the tools to install and work just fine in CS5 by manually moving them from the old CS4 plug-ins folder.