When I purchased my router almost two years ago, I’d hoped to be able to install a third-party firmware (dd-wrt, openwrt, etc). It turned out that the WNDR4500 was sufficiently different from Netgear’s other similarly numbered models that it was not supported.
From time to time I checked various forums to see if there had been any progress on support and was surprised (and delighted) to discover this thread on the dd-wrt forums leading to these firmware images.
I installed r23040 using instructions found on the internet, which worked (huzzah!). I’ve been able to set up one of the wifi channels in client-bridged mode which isn’t possible with the default firmware, but is a configuration I’d hoped to be able to use when I first purchased the router.
dd-wrt makes messing around with network configurations remarkably straightforward. I’ve yet to try the USB support or anything beyond basic routing.
There are some bugs, and some minor problems that are probably due to my own misconfiguration, but no show-stoppers thus far.
Like many projects of this nature, “documentation” seems to consist of group-edited wiki pages that can be inconsistent, out of date, and unclear, web forums where the discussion assumes a far higher level of familiarity with the subject matter than is useful for the casual newcomer, and an assortment of blog posts.