I recently replaced the Atheros WiFi card in my Fujitsu U2010 with an Intel 5300 AGN half-sized Mini-PCIe card. The default Atheros Wifi card in the Fujitsu does not support MIMO and 802.11n on the 5 GHz band. This is a real let-down for a (draft-)N card.
Luckily the Intel 5300 AGN is one of the very few cards that are available in the half-sized Mini-PCIe form factor, so it fits into the Fujitsu U2010 and U820.
The process is quite involving and not for the faint of heart. Here are some snapshots of the process: