I just learned about this nifty tool from Ren & Stimpy fan Jeff Pittelkau, an esteemed friend and former colleague. LogMeIn provides secure remote-control access to your Mac(s) and PC(s) from any Web browser. Very handy -- and, at it's most basic level, also free.
To use it, you create a user account at LogMeIn and install a small application file on each computer you want to control. If you plan to use specific computer(s) as "command center(s)," you can install an optional Firefox plug-in on them to streamline the LogMeIn log-in process, but any browser will work, plug-in or no plug-in.
When you log in to your account, LogMeIn shows you a list of the client computers you've configured. Choose the one you want to drive, enter your user ID and password for that machine, and the desktop of the target computer appears in a browser window. Mouse movements/clicks and keystrokes within that window affect the remote machine. So you can launch and close applications, move and rename files, etc. You could, for instance, open Gmail on the remote machine and email a photo to yourself (or anyone else). You can't, in the free version of LogMeIn, download the file directly to the computer you're using to drive the remote machine, but a (PC-only) pro version of the software enables drag-and-drop file transfers, local printing of documents on the remote machine, and other cool features.
Special controls in the LogMeIn window let you adjust output volume on the target machine, save shortcuts to folders and applications you access frequently, and force-quit applications on the target machine (needed because typing CTRL-ALT-Delete, even in the remote-control window, will trigger force-quit on your local computer, not the one you're controlling).
The speediness and responsiveness of the remote computer will vary, presumably with the speed/bandwidth of your Web connection. There's a little sluggishness, but nothing that makes it unusable. After all, this is an "I need that in a pinch" kind of tool; it's not meant for long work sessions. I've set it up so I can safely access my own Mac, and I plan to install it on my dad's MacBook as well, so I can help him troubleshoot occasional glitches.
Thanks for the tip, Jeff!