An exciting and very-nearly-as-good sequel to the classic I hate routers!
After that last little debacle I've been carrying on running the old WRT-310N, but today it finally narked me off sufficiently again. The wireless congestion in my area is just nuts now: I can see 26 wireless networks from my laptop, all in the 2.4GHz band. Even with the best config tweaking I could do, I just couldn't get wireless transfers past 2MB/sec or so - that's a third of the 802.11g nominal transfer rate, never mind 802.11n.
So I did a bit more research, and this time I went out and got a WNDR3700 from Netgear. It's about the highest specced consumer router you can get, and has all the features I was looking for (again): gigabit, dual wireless frequencies, and dd-wrt support. Actual documented dd-wrt support from lots of keen users.
Got it home, plugged it into a single system to configure it, and found I couldn't get to the router's address. At all. Got frustrated for half an hour. Tried a different system, and it worked. Huh. Flashed it to dd-wrt, following all hopping-on-one-leg-wearing-wellington-boots-under-a-full-moon-while-sacrificing-a-chicken router flashing procedure, swapped it out for the WRT-310N, saw everything come up, then noticed it didn't have a WAN connection. As I started to investigate why, noticed that suddenly all network communication completely ground to a halt. Tried power cycling it a few times, and the same thing would happen - no WAN connection, then no connections at all in short order. Tried transferring a file from my laptop to my desktop right after startup, just to see how fast the wireless was - transferred 1MB and then all connections ceased.
Cursed colorfully for a few minutes, then ripped the thing out and put the WRT-310N back in. Entertained wonderful destruction fantasies, but eventually calmed down enough to go trawling through the dd-wrt forums, whereupon I came across this gem (Fedora bug report here). Apparently this particular new-hardware-quirk is not just the universe hating me, but a widely reproduced bug: Intel somehow managed to stuff up their wireless drivers in kernels 2.6.39 and later such that connecting to many dd-wrt router configurations produces exactly the Sudden Death Effect I was hitting. Switched the WNDR3700 back in, booted my laptop back to kernel 2.6.38, and lo and behold, the report's bang on: the local network now works great, and I can actually transfer files from my laptop to my desktop at 10MByte/sec! It's not exactly 300Mbit/sec, but it's a hell of a lot better than a kick in the teeth. Thank you, 5GHz band, thank you.
I still don't have a WAN connection, though. No worries - that turns out to be just a simple case of power cycling the modem. Simples.
So finally I appear to have a working dual-band router setup capable of vaguely decent wireless transfer speeds. Fingers crossed. I highly recommend that 802.11n config tweaking guide I linked to earlier, btw - it has lots of good tips for actually achieving 802.11n connections. Like you have to configure for WPA2 only, with AES encryption only - don't use mixed mode, don't use TKIP. Only use channel 1, 6 or 11, and do a site survey (dd-wrt has this feature) to see what channels other local wireless APs are on. Don't use 40MHz channel width in the 2.4GHz band unless you live in the middle of nowhere, because it's all but guaranteed to be impossible to find enough free spectrum to manage it. But if you have the kind of 2.4GHz congestion I do, nothing's going to help, really. A dual-band router is a really good idea, once you get it running. I've set up a G-only, WPA1/2 mixed, AES/TKIP mixed AP on the 2.4GHz band for compatibility, and an N-only, WPA2-only, AES-only AP on the 5GHz band for security and speed. Definitely seems like the way to go.