This downloaded on my home pc last night. Anyone know if it is safe to install?

lots of contraversy

Here is what some are saying on technet:
Microsoft will resume rolling out Windows XP Service Pack 2 (SP2) Wednesday when it starts pushing the massive update to business users via Windows Automatic Update and the Windows Update Web site.
Although Windows XP Home Edition users have been downloading the security-oriented upgrade since last Wednesday, Microsoft put a hold on updating Windows XP Professional systems due to concerns by businesses which didn't want their users installing the service pack.

Faced with enterprises worried about SP2 hitting desktops before IT had had a chance to properly test the update, Microsoft two weeks ago released a toolkit that walked companies through the process of setting a Windows registry key that skips downloading SP2 for 120 days, but still downloads other critical updates.

Tardy businesses still eager to block SP2 can download the registry-setting tools from here.

Microsoft has also posted a script to its TechNet Web site that companies can run to block or unblock multiple machines on the network from accessing SP2.

Delaying SP2 deployment is a smart idea, according to many analysts. Gartner, for instance, has recommended that enterprises wait at least two months before rolling out the update.

More on SP2.
Here is a pretty good article on SP2. Most of the concern is from large enterprises who have custom code that depends on drivers or scripts to be consistant on every machine in the organization.

http://www.pcmag.com/article2/0,1759,1639618,00.asp