Running any unpatched OS online *especially* windows is like painting a sitting duck target on your machine for exploits.
This holds true for many OS's, but not windows. Have you actually looked at the critical patch list for windows? 99% of the patches are for vulns within programs that people don't use. WMP, Office, IE, a dozen other programs from the year 2000. There's no reason to patch XP unless you enjoy constant slowdown on the machine. You're no more at risk from stupidly obscure 'sploits than the next person. Not to mention that half the windows patches introduce more vulns than they fix.
Any patches that you really need to apply you'll be prompted to apply when you run the app that needs the patch. Like Adobe Reader (fook knows why anyone uses this anymore when foxitreader is better and has less overhead, but I digress) or Flash.