Lee, if you're an experienced photographer, which I know you are, then you also know it's best to shoot in the highest resolution, uncompressed, period!
But hey, if you want to able to shoot more shots with your camera, then you always have to turn to a compressed format or buy more storage.
Gare's 'Megabytes' rule works if you know what you're going to shoot or scan, but hey, photography can be unpredictable. I had shots that I wasn't satisfied with, until I cropped a certain area....et voila! Suddenly I had a great shot. But where does that leave you if you shot the image in a low resolution?

Also, maybe now your target is a 5x7 print, but what if someone comes to you one day who wants a larger print of that same file?
Personally I never shoot with TIFF. I don't see enough difference between TIFF and the highest quality Jpeg that urges me to buy an extra 200GB hard drive or to archive my images on 150 CD?s.
Just a simple example of what it means to shoot and archive in TIFF;
2,000 JPEG images of let?s say 2M take up 4 GB of CD storage
2,000 TIFF images of 50 MB each, that?s 100GB! You?ll need a lot of CDs/DVDs for that!
And we DO need to archive them or don?t we
Ok, back to the subject... my suggestion
- shoot in the highest resolution
- select the quality (raw/tiff/jpeg etc) that suits your storage
- transfer your images to your computer and make the necessary adjustments
- most of the time you can leave the 180 dpi intact if you?re printing on a home inkjet and that?s it
There are many other ways to do it, but this one is quite straightforward.