I've been interested in the extended functionality a Linux-based router can give but haven't found too many easy instructions on how to do this.  An example of what can be be done includes increasing the transmission power for greater range. 

" Under the Wireless>>Advanced Settings  tab, DD-WRT has a customizable setting for transmit power. Labeled "Xmit Power", this entry is 28Mw by default, but it can be set anywhere between 0 to 251mW. The "Help" menu indicates up to 70mW is safe for improving range. Raising the power level above that, they warn, may generate excess heat in the chipset, which could shorten the life of the router." (Linksys WRT54GL Linux-Based Wireless Router, Extreme Tech). 

For complex set ups involving VOIP or Wi-Fi hotspot this may be a good solution for adding important functionality