Have you ever wished you had TCP/IP printing available from your Treo (or Windows Mobie or PocketPC device)? Probably not, but if you did, you could use PrintBoy. PrintBoy is a nice little program that allows you to print to network-enabled printers from anywhere you have an Internet connection. And, it integrates pretty nicely with Documents To Go.
It's a little pricey at $50, but I guess this is kind of a niche solution. It's actually very handy if you need to send a hard-copy of something from your Treo to someone in your office while you are on the road.