The new Macbook Unibody has about five ports. In my case, all of them are full all the time. Unless you buy a hub, why not use that defunct G5 for additional ports and devices? You may save some energy by not relying on a large number of external devices (keyboard, monitor, hard drives, etc.) or AC power. I was also tired of the issues with a USB powered Oxygen 8 keyboard from M-Audio. Using my G5, the VNC access is actually somewhat tolerable for light operations at reasonable resolutions. If you have your Mac configured with a SATA II card and an internal drive mounting system, you can have access to more drives at decent speeds.
These instructions cover setting up a FireWire 800 link, a MIDI Network Link, VNC access using Vine Server, which is much faster than ARD. Also, you can easily use your G5 as a bridge to connect to two-pin devices (most video-cameras). Latency is minimal and the data path is more than sufficient, if all other interfaces are disabled it is also somewhat secure. These instructions also go over the issues I have encountered, and specific Cocktail features that aid in VNC/file access.
What you need is a Mac running 10.4 or greater with a working monitor and video card. If the video card doesn't work, and you turned have remote access via ssh/telnet on, then you're in luck -- check out this hint Works great, then you can set up the Vine server and disable the Apple remote access server (be sure to use a different display number on the Vine server.)
Cocktail is required, and you can optionally use Vine Server and Chicken of the VNC. You can easily use any VNC server, including the built in one, as well as any VNC client. I've tried a few combinations, but I enjoy this one the best.
Restarting/Automatic Login
When you restart, if you have automatic login disabled you will need to login, and dismiss the 'no keyboard monitor attached' dialog. Even if you do have automatic login, you'll probably have to dismiss this dialog. Setting up the server to mount disks without user login (under Disks » Misc) is very helpful.
Video Issues
If you do not have an AGP video card installed, then many applications that rely on openGL or quartz extreme (FCP and Motion, for instance) won't run. QuickTime and VLC work, but video playback isn't full-speed (it's about half-rate.) I have also successfully used eyeTV with the dongle by ElGato to share recorded episodes and flip through channels (at a very high latency).
VNC Specific Issues - Cocktail Configuration
I noticed the biggest boost when turning off the Desktop in the Finder using Cocktail, and using a 1024x768 screen. While for many this takes getting used to, I run like this on all my computers now, and find it's easier to organize files without it. Remember that when you click on the Finder icon, it will either bring a window to the foreground or make a new one. Use Cocktail to disable all those interface tricks as well. Millions/thousands of colors doesn't seem to make a difference, and it usually doesn't work properly with many applications.
Firewire Device Behavior
Take care when plugging in FireWire devices. By default they will appear on the shared Mac (meaning not the G5.) To mount devices on the G5, first disconnect the FireWire cable from the client Mac, connect the device to the server, wait a brief moment, then reconnect the client and resume operations.
Step by step Run down
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090706005356831