Info here
http://www.krebsonsecurity.com/2010/02/new...ndows-xp-users/
Now narrowed down to one particular patch ... http://www.theregister.co.uk/2010/02/11/ms..._update_glitch/
I installed these updates yesterday, and I haven't noticed any problems yet, even with a computer restart. I guess I must be one of the lucky ones.
Neither of the two systems I updated have any issue. Luckily though both have Macrium backups should the need arise to rescue them!