You could search here and see the many threads by people that have had problems, and probably nearly as many from those that haven't!
SP3 isn't a Critical patch (unless you haven't been doing routine patching) and any 'improvements ' it provides appear to be limited to those that have networks, Full details can be obtained from the PDF document that you can download here;
http://www.microsoft.com/downloads/...AD-BC34-40BE-8D85-6BB4F56F5110&displaylang=en
This is Microsoft's own summary of what it contains;
"Windows® XP Service Pack 3 (SP3) includes all previously released updates for the operating system. This update also includes a small number of new functionalities, which do not significantly change customers’ experience with the operating system."
I myself haven't installed it because a) I'm still on dialup and it's a very big d/l, and b) I don't want 'all previously released updates'. I use the Custom option when doing updates and only have the Critical ones. I have no use for .NET framework, Silverlight or any of the other goodies MS think I need.
I have seen suggestions that it will be mandatory in the future in order to obtain updates for XP. I doubt that that could include future Critical updates but will wait and see.