I don't know about being obsolete. It's always been PAN hardware and probably will still have a foothold in that sector moving forward. Beyond the obvious similarities the two technologies aren't serving the same purposes and aren't all that comparable. There probably are some graphs out there showing things like Direct Sequence (wi-Fi) vs. Frequency Hopping (Bluetooth) and so forth though.
CCNA, MCSE, A+, Cisco Certified Wireless Field Engineer
Bluetooth and 802.11 aren't really competing technologies. Bluetooth is meant for wirelessly attaching small personal objects, like cellphones, PDAs, keyboards, mice and other user interface devices. 802.11 is meant more for connecting computers together or to the Internet without wires.
The main reason Bluetooth might be replaced in a couple years is Intel's deciding to make and push Wireless USB as a replacement for Bluetooth.