When I set up this website last year I had a bit of a steampunk vibe because of the new Doctor Who series, which lives on in my lab. I thought about updating the blogs to have the same look, but I didn't.
Then Tron came out and although I didn't go to see it I changed my Windows 7 desktop wallpaper to the one in the architecture set that was the Melbourne link gateway bridge at sunset as that had the same sort of neon feeling.
Then in spring I changed my wallpaper to the Selfridges building in Birmingham.
So to answer the question, probably never.
Photo from mar00ned.