I have seen the same thing here as well. The updates have been taking longer than normal and sometimes the percentage will either backtrack or simply sit at 0% Completed and then suddenly go to Installing.
System is P4 with WinXP.
Also , no updates for the past 2 days. When I try to manually do it , it comes back with "your software is up to date".
Do you have some web browser toolbars? Most of them don't let McAfee update correctly. Remove all of them and try to manually look for updates.