Apple has announced that you shouldn't be running Time Machine if you are using Aperture unless you're in manual mode. This got me to wondering how I used manual mode in the first place; Google helped me discover that a right-click on the Time Machine icon in the dock offers a Back Up Now option, which does just what you might expect. Using that feature, it appears that you can turn the big Time Machine switch off, and still do manual backups ... which brings me to my hint.
If you are using a laptop and have a network-connected drive with your Time Machine files on it, you may find that backups are somewhat unpredictable, in that they don't seem to happen automatically. You'll find this especially true if you did the first backup with a wired connection, as your machine will then never back up over wireless. This turns out to be because, on a network drive, Time Machine creates a sparse image (an expandable disk image) with the MAC address of the machine in its name. Then, when you're on a wireless network, Time Machine doesn't find the file, as the MAC address has changed.
These images have the form of Machinename_012345678abcdef.sparseimage. If you make a symlink with your wireless MAC address to the existing image, then Time Machine starts working again. Then you can turn off automatic backups, and just do a manual back up every day when you get home.
[robg adds: I haven't tested this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2007102814522699