I am sure this has been posted and many already know about it, but I thought I would mention it again just in case its helpful. Pretty cool stuff! you can get VPN working and the ability to access your home network from off-site is very cool...
DD-WRT is nice, but you olny optimize the software in the router, check the 600$ router will actually have no problem working with complex routing tables and truly support more than simple routing protocols.
I found out in mine that i had issues with torrents and more than 200 simultanous connections.
but still is a nice project when you have a 50$ router.
Memory will likely be the problem. Depending on the device that you have, you may be able to fix the memory a bit. Some of the Linksys models are shipped with half of the memory crippled and you can open it back up again.