Actually it's not too bad. I have set both mine and my wifes home machines up to use user accounts and it doesn't cause any issues except when a new app needs to be installed.
To install an app I log in as the admin and run the install. I then log out of admin and into the normal user account and test it. If the app fails, the sure-fire fix (hasn't failed yet) is to reboot into safe mode (only way in XP Home); log into admin again and change the programs install directory security settings to allow full access by the user accounts. Reboot, and test as user again, voila! Sometimes older programs won't set up programs in All Users, so a copy of the folder so it shows up under the program menu is sometimes required.
This is a little convoluted, agreed. But it happens once or twice a year. Malware can happen at any minute you are logged in and connected to the internet. Well worth the hassle.
Updates are done as Admin and usually propogate across all users (Firefox seems to be finally fixed so this works, or maybe I have learnt to turn off the auto-update).
But wait.... You say that I am now vunerable to attacks that modify the programs in that folder. Well the chances of hackers attacking these (generally older) obscure apps is pretty low. The whole small install base therefore not worth effort argument.
