Happens all the time. In LA, Activision bought all the bus benches in front of EA's building in Marina Del Rey to promote Call of Duty and Gun back in the day. Hell, Sega bought the billboard in front of Sony's building in Foster City back when the Dreamcast launched to make fun of Sony's PS2 production delays they were experiencing at the time.
There's one near the Eidos Montreal office, too.
EDIT: Damn it, beaten!
Took that picture when I came out of the office earlier... That white/grey building in the background is the Eidos Montréal office
The ad is great but the flag on top is an even nicer touch.
Do UbiSoft and EA really compete in the same genres though?
Shhhhh. This is point and laugh time.