Live OneCare completely borked two of my systems. On one of them (a Core 2 Duo w/2GB of RAM) it made it so that even opening up a folder (like double-clicking on My Computer) took 15-20 seconds for it to respond, and would spike the CPU to 100%. Everytime I would try to reboot at least one component of it would crash and cause me to have to physically kill the power. On another machine that was having internet problems (which I later determined were related to OneCare-it takes over the Windows Firewall by the way, making it nearly impossible to manage) it kept telling me that it was out of date and needed to be updated before it would keep working. I told it to turn itself off in the mean time, it said it couldn't do that because it was out of date, and got stuck trying to update itself, until it had sucked all of the resources of the PC completely dry. It also broke all of my XBOX media center connect stuff.
In other words, for me, it wasn't worth the $20 I paid for it, and I would gladly pay another $20 for someone to erase the memory of this POS software from my brain.