Tonight I booted up a 2008 MacBook with a dead screen after hooking it up to an external monitor, waited extremely long until the thing had actually booted, got logged in automatically, and noticed how the whole thing was extremely slow. I spent about half an hour disabling all of the useless crap the previous owner had installed on it (including Flash Player and about every single remote desktop software that existed for the thing, all active and with no password protection*), ran Disk Utility twice in a row, deleted all wireless networks it automatically logged on to (95% of which were insecure), and then discovered that it hung when trying to access the printer preferences. Removing the printer driver that was installed twice (both active) lead to a considerable speed up, and got rid of about 250 Mb of RAM usage. One reboot later and it was considerably more nimble.
* What's the use of the firewall if you're going to leave a machine wide open by any other means possible?
The worst thing is that this was owned by someone who has a technical university degree and otherwise isn't a stupid person... 🙄 They still want their data, so the next step is to get a USB stick, back up the data, and then wipe and reinstall (which should rid the laptop from the remaining crap that can't be uninstalled). And do something about the cleanliness, too. Yuck.