I don't use my computers to their maximum potential, but we run a pos, (write all our tickets, barcode merchandise, etc), Quickbooks (bookkeeping, invoicing, etc.), Works and Picture It publishing (for all the little arty projects we do, also e-newsletters).
We use the internet to look up prints for customers; it is so easy with a cable connection.
We also answer e-mail from customers, and inquiries generated from the website.
My husband scans in his 35 mm slides, uses Adobe Photoshop (soon to be 8., I guess) and prints his pictures. We sell those pretty regularly, so it's very handy for that application, although I don't really have the patience or desire to learn it.
I place some orders online, but not all.
It's also good for Grumbling, though I usually save that for "home".