I've been running Tomato USB on my RT-N16 since December. I love it!
The only issue I'd like to resolve is the USB attached storage speed is so slow. +/- 1.5MBps
This is across multiple enclosures with ext3 and NTFS over wired and wireless connections.
What can I do to increase the speed?
That does sound excessively slow. You should get about 6 MB/s as shibby20 posted. What transfer protocol are you using? A couple of weeks back I was having a problem where occasionally my SAMBA speed would drop by a factor of 8 and remain low until I rebooted the router. However, my HTTP and NFS transfer speeds remained high. I searched FAQ's everywhere, with no luck in finding the solution. Then I noticed my the process I had scheduled to auto update optware was going into some sort of failure loop and consuming 100% of the CPU. I removed that job from my scheduled processes and I have not seen the same problem since.
You'll find the daemons some protocols require much more CPU than others. If you have nothing else running, you should still see about equal transfer speed on most protocols, but as soon as you have a second job consuming a significant amount of CPU you'll notice the difference. The NTFS drivers in Linux are one of those things that use a significant amount of CPU, so try and use ext3 as much as possible. If you want to occasionally plug the drives directly into a windows box, there is an ext2 driver that works fairly well for windows. ext3 is backwards compatible with ext2, only when there will be no journalling when connect to the Windows (unless the driver has been updated to include that now…).