I picked one of these up about a week ago now. Wireless N speeds have really disappointed me (speed reported by the rt2870 linux application fluctuates between 54, 81, 162 and 216 Mbps, but real world testing gives me a maximum of less than 1MB (8Mb)/s so...yeah) but in all fairness to the device I have it at the other end of the apartment with several walls in between it and my desktop.
Having seen the bad rap the download master software got didn't really give me much pause as the next thing I noticed while googling the device was this site: wl500g.info - the replacement firmware on the site adds some new functionality (a samba server for actual SMB (or what microsoft like to call windows file sharing, even though they were only one of the companies working on the protocol - kinda like "Microsoft" tcp/ip in your network device properties etc)). I can understand being a little wary of grabbing random firmware put together by some guy on the net but after flashing my device the only discernable difference was the new options on the admin webpage (and the lack of download master options). Stuff added includes igmp, better printing support, and a feature any tech-head would love - telnet and ssh access to the linux OS running on the box itself.
From here you can run a script to install a program called ipkg which reminds me a lot of apt-get for debian-based linuxes. For anyone who isn't familiar with it, basically what it does is gives you access to x thousand (where x is not a small number) programs written for linux, and handles installing, upgrading and removing them. Ipkg does basically the same thing, albeit with a much smaller package base - but even so, there is generally a few different options for any given task. This turned out to be quite a good thing when I couldn't get transmission (the most popular bittorrent client by the looks of things on the wl500g.info forum) to mesh with the web interface properly. I ended up using a program called rtorrent running on the wl-500w and a java frontend for it called ntorrent running on my kubuntu desktop. Performance seems pretty comparable to ktorrent running on my desktop machine, although running them both at the same time seemed like a recipe for maxing out my adsl modem's connection pool.
Ipkg also lets you install samba for windows-like filesharing. It can do things like restricting share access to set IP addresses and a bunch of other stuff I've never had any reason to use.
Being as it is a mini version of linux running on the router you can do a whole bunch of other stuff with it too - there are reports of people hooking up usb soundcards to it and using it to play back audio from shoutcast streams. I'm currently eyeing my leadtek winfast dtv gold usb dongle (which I know works under linux, I'm using it on my desktop atm) and planning to try to get it and the router working as a PVR in conjunction with the 750gb hdd I already have hooked up to it. Not sure how the cpu in the router will handle the load, but with a bit of luck it will be beefy enough to handle a straight dump to the hdd with no processing on the stream without say freezing up anything else the router should be doing.
Hmm...this was going to be a one paragraph reply to let you know that you shouldn't necessarily write the wl-500w off for torrents just cause download master sucks for bittorrenting. Damn Coffee.