At 1337pwn.com, we started seeing the trend over the weekend. From our data, it looks like Call of Duty 4 is poised to retake the top spot on XBOX Live.
1. GTA IV (1000)
2. Call of Duty 4 (999.56604756119)
3. Halo 3 (849.8524561708)
Considering that Call of Duty 4 recently surpassed 10m copies sold, it's hardly a surprise as it manages to be dominant on both the PS3 and XBOX 360.
UPDATE: 1640EDT
COD4 is now back at the top on XBOX Live.
1. Call of Duty 4 (1000)
2. GTA IV (998.01518812565)
3. Halo 3 (853.6416983086)
don't pwn alone(tm)