Any XP exploits that are also in Windows 7 (etc.) will be fixed in Windows 7 (etc.) so there shouldn't be too much risk of infection if you keep your machines updated.
I emailed all staff recommending they upgrade, disconnect their XP machines from the internet, or assume that they are compromised and all their data could be lost at a moment's notice. We've since recommended a few new machines to staff in the last fortnight! (The Zoostorms with dual-core Pentium & 4GB RAM + a Samsung 840 EVO 120GB + Win7 licence is a surprisingly cheap and competent option.)
Upgrade to 7/8.1 .
I've just set my Win 7 wallpaper to XP Bliss. It just seemed fitting on the Death Of XP Day....
Bear in mind that Windows 7 is fundamentally more secure than Windows XP as well thanks to its underlying architecture.
At the end of the day - if people have XP at home, what can you do? If you tell them not to bring memory sticks in from home anymore, that'll last a fortnight until they need to bring reports in, then they're not going to care about your network, they're only going to care about not having to retype those reports.
I've scaremongered to encourage upgrades, and to be honest, if a machine is old enough to have come with Windows XP it's old enough to make an upgrade worthwhile, but still - I'm essentially powerless to stop anything happening. Even if I could ban memory sticks, they'd get a virus that emailed itself to all contacts, including their work address, and then they'd open the attachment...
The Hilton hotel by the NEC in Birmingham still uses windows XP
I remember thinking at the time I wouldn't be able to learn XP as my home PC was too old (1997 vintage in 2001) but then got hold of some scrap PC parts for the bare minimum spec... AMD K6 233, 64MB of SIMM (!) RAM, 2GB HDD and case sides made of sheet metal because the originals were missing. That machine ran pretty damn well for a good year or two until (lack of) disk space caught up with it :p
I seem to remember downloading all the (then Whistler!) XP leaks. Many disliked the Fisher Price interface but when you were following the beta / RC process and that was suddenly introduced I was quite blown away by it all!
Watercolour theme (which was based on the theme Whistler came with) was pretty cool too.
85% Of 800,000 NHS still are on XP (i'll see if i can find the source for this)