Adobe Photoshop CS (v8.x) no longer supports displaying PSD files as thumbnails in Windows Explorer's thumbnail view, all you get is a standard Photoshop icon. The read-me file for Photoshop CS confirms this.
Photoshop CS no longer provides thumbnail icons of .psd files through operating system folder windows. Please use the File Browser to view your .psd thumbnail files.
If you have upgraded from a previous version of Photoshop to Photoshop CS you will be OK but a fresh install of CS will NOT included thumbnail previews of PSDs. However I have discovered how to fix this, all we need is a missing DLL to be placed in the right folder.
Download psicon.dll from DLL Dump
Place the DLL in C:\Program Files\Common Files\Adobe\Shell\
Thumbnail previews of PSD files are now back
Simple but essential functionality. It does make you wonder why Adobe saw fit to remove the thumbnail preview in the first place!