We have a programmer that was having a lot of problems with his XP machine that started around the time that the April patches came out. It acted much like XP acts when it has the April updates along with either a bad nVidia driver or bad HP package. We ended up swapping hard drives so he could keep working and I set aside some time to dig into what was going wrong.
Long story short, a month or so ago, he installed OpenLDAP on the machine and had it setup to start as a service. I'm not sure how or why the system would boot up correctly previously and maybe the April patches changed the order in which various pieces of the OS came online. Either way, when you would try to log in to the machine, you would be stuck for an hour or 2 at 'Applying user settings..."
After it times out, many services failed to start up and OpenLDAP was hung in 'Starting'.
I understand why now - OpenLDAP had stolen the default LDAP ports and effectively killed any useful Active Directory activity. Disable OpenLDAP in safe mode, and the system is happy as a clam.
