Currently, the iPod Touch uses an 802.11b/g Wi-Fi chip. But that may soon change as Apple is laying the groundwork to introduce high-capacity, low-power 802.11n Wi-Fi to the iPod Touch. Not only is it news for the iPod Touch, but even the iPhone might get it too.
This change would be a huge improvement to the old 802.11b/g chip which has a throughput of less than 25Mbps on the 2.4GHz band.
These are good news, the bad news is, you probably have to buy a new Touch with the new hardware. This is primarily essential as both devices would also need to change or upgrade their processors to accomodate and support the new 11n chip.
The 3.0 firmware is due to be released this summer, and speculation is circulating that it may coincide with new models of the iPhone 3G and iPod Touch.