I have an old Linksys WRT-54G v3. I have ran various different firmwares over the years, but performance was never a big deal. I was mainly looking for something that allowed to me to access all of the devices features and a nicer frontend than the one that Linksys provides. At one point I was using different firmwares for QOS when we were sharing our connection with some other people in our building. Anyways, I had been using X-Wrt (white russian) for quite some time. It is basically a nice user-friendly version of OpenWrt.
Recently we purchased a Squeezebox Duet and even more recently we purchased a second Squeezebox Receiver. We finally have wirelessly-streamed music in pretty much every room of the house. We had been noticing gaps in the audio and I decided it was finally time to fix it. I discovered a diagnostics page (called "Server & Network Health", available via SqueezeCenter's Help page) and noticed that streaming rates I was getting were much lower than the 3000 kbps that I was expecting. In fact I was actually getting much lower than 1000 kps and had to change the scale of the measurement just to get a proper reading.
I decided to upgrade to Tomato firmware, which I had heard a lot of good things about. Immediately, I was getting about 3000+ kbps and the audio problems were gone. As an added bonus, we are now able to watch MythTV from a wirelessly-connected laptop, which were not able to do before (previously I had assumed that wireless streaming video was just too much for today's wireless networks to handle, or too much for MythTV to handle). I think I am going to make a donation to Tomato because it has made such a big difference for us. We can now enjoy listening to our mp3 library anywhere in the house (without gaps) and can watch recorded TV shows on our laptop.