For some reason, Microsoft has never seen fit to implement network sharing of scanners as it has printers--the reason RemoteTwain ($29 for personal use, $59 for business use; 14-day free trial) and similar software exists. If you're scanning a single page, or a multi-page document that fits in the scanner's automatic document feeder (a paper tray for scanners) why shouldn't you be able to scan from the comfort of your own PC and work on other stuff while it proceeds? This scenario is common enough, and RemoteTwain facilitates it.
RemoteTwain is really two programs. The SharedScanner module sits on the PC with the direct-attached scanner providing access, and you install the RemoteTwain module on any PC from which you want to scan remotely. There's nothing to indicate that RemoteTwain is installed. You'll only know it's there when you see it listed as you scan from a program such as Photoshop or IrfanView, or, "acquire from Twain" in the lingo. You'll find this info in the readme.txt file--there's no other help at the moment.
RemoteTwain worked quite well, though it requires you to enter the IP address of the PC with the SharedScanner server on it. E.g. 192.168.1.65. There are also some rough edges. For instance, you must hit the "connect" button each time before you scan and the DPI drop down menu offers every DPI setting from 50 to 6399--in increments of 1. It's actually easy to scroll through, but limiting it to a few common DPIs such as 150, 300, 1500, etc. then allowing you to type in uncommon ones would make life a bit easier.
With some scanners you'll also see a WIA (Windows Imaging Interface--a Windows bridge for Twain) version of the scanner listed. With my Epson Perfection 2480, I was able to scan in color only with the WIA version.
There's one other thing that's a bit puzzling. Vendor Scanworks Software bundles RemoteTwain with WebScan, a program which uses your browser, Microsoft's Silverlight, and a portal at the company's Web site to create a scanning application. It's actually a separate product, yet when you click on the SharedScanner desktop or system tray icon WebScan is what launches. You must right-click the system tray icon and select options to actually see and configure the SharedScanner module--something you probably won't need to do. I'd prefer a more separate approach, or at least make SharedScanner the default.
All told, RemoteTwain is a nice, affordable solution for the odd occasion when you want to scan remotely or if you want to keep an eye on scanning activities in a small business by funneling it all through a single unit.