According to
this article on TechTV the 108Mbps speed most likely comes from channel bonding where multiple channels are combined to get a faster throughput. It's very similar how back in the days of dialup, you could use 2 modems to get a faster download by combining them together. The problem with channel bonding is that any neighbors that have wireless will be affected. They also go on to say that Linksys' Speedbooster technology won't interfere.