I will save as a PSD if I think I might want to do more edits on the
image, but mostly flatten the image when I am done with the edit and
save as a high quality jpeg.  I don't know that there is a big
difference between tiff and PSD I use PSD since it is the native format
for Photoshop.

I don't normally keep the PSD file around just because it takes up a
lot of room and if I really want a different edit of the image it is
simple enough to start over with the raw file.  Most often if I am
going to redo and image I will want to change how it was converted
anyway.

Scott

-----------
I save my edited raw files in PSD format.  Usually I have layers and
selections/masks that I wish to preserve.  The PSD file isn't re-sized or
sharpened -- those actions are output dependent, so I open the PSD file,
finish the editing as required and save the results as a  JPG for display or
printing.  The PSD files are saved in 8 bit format, because all the
colorimetric editing is done in 16 bit by the RAW converter (Lightroom or
Rawshooter Pro).  16 bit offers negligible benefits for the remaining
editing that I do in Photoshop.
Regards, David "Routemeister" Thompson
http://picasaweb.google.com/david.routemeister

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I use PSD as an intermediate formt as long as I am working on the
image.  After I'm done, I save the "post-processed original" as an
unsharpened 16 bit PNG, and in most cases I then delete the PSD.

I prefer PNG over TIFF (also lossless), because PNG is a more compact.
I also convert RAW data into DNG for archival purposes.

I.e.: I archive two versions of each image.  A DNGa PNG which is the
result of post-processing (i.e. WB, levels and curves).  My archive
is stored at hard-drives at two separate, secure locations (not RAID
yet, but I'm getting there).

The PNG is then used as basis for generating production copies in
various formats (e.g. JPEG for web, TIFF for most print, PDF for some
print) .  My final step from the archived PNG to production images
always consists of the following five steps in that order:

1. Resize
2. Set bit depth
3. Set colour space
4. Sharpen
5. Save as desired format (JPEG, TIFF or PDF)

I also keep a web-sized JPEG around for fast browsing, but that is
not part of my archive, and I sometimes leave the PSD behind to have
layers and masks at hand if I feel I might do some more work later,
but the PSD is not archived.