Market research firm NPD reported that U.S. sales of video game hardware and software rose 47% from a year earlier, mostly attributed to Take-Two Interactive Software Inc's Grand Theft Auto 4 and Nintendo Wii console.

The popularity of GTA IV did not boost sales of Xbox 360 and Sony PS3 consoles. Actually sales numbers fell sharply from the previous month.

U.S. gamers bought 188,000 Xbox 360 and 187,000 PS3 consoles in April, which is down from 262,000 units and 257,000 units in March.

The Nintendo Wii managed to sell an amazing 714,000 consoles in April. Wii fans bought more than 1.1 million copies of Mario Kart Wii making it the number 2 game in the month behind GTA IV.
GTA IV launched at the end of April, so I think the full impact of the game will be seen in the May sales numbers.
Via this Reuters report.