That's what happened to Google Personalized Homepage for some users today. Says Michael M.:
Today, I logged on at college and all was fine on my homepage. When I got home, I turned on my laptop and my homepage had reverted to the default, with all of the default gadgets and the default theme. I tried to re-add my gadgets, but it keeps going back to the default style. I've tried clearing my cookies/history and signing in/out.
The personalized homepage is the page I visit most on the internet, it tracks all my news and weather and lets me keep track of my schedule and chat to my friends on Google Talk.
My homepage looks the same, but there's a big thread at Google Groups with people who lost their homepages. Google's answer is so endearing:
We're now in frantic-chase-down-this-bug mode here at the Googleplex, and I hope to have more info for you soon. For now, we're not entirely sure of this, but it's possible that changing your homepage theme might cause the problem. SO, if you still have your homepage intact, please avoid changing your theme until further notice. The big question I know you'll all want answered is whether you'll get your homepage back once we sort things out... and the really honest answer is that I hope so, but I just don't know yet.
Update: A day later, everything was back to normal in the Google land.
{ Thank you, Thomas, Redmar, Yasar, Michael, Joe. }