Most normal programs don't use /cache.
To fix your cache market issue:
busybox mv /cache/download /sd-ext/download
ln -s /sd-ext/download /cache/download
If you don't have a sd-ext you could use /sdcard/download instead. The directory will already exist if you've downloaded anything from the browser, so I just remove /cache/download before linking. I used to get package file invalid errors from this setup though...
Ti backup will also let you move stuff to /system and re-odex your rom instead of shrinking /system. Sure, everytime system stuff updates you need to click a few times, but unless space is real tight, it works fine. The re-odex-ed rom seems to boot faster for me than with external dalvik-cache, too, but that could just be me pretending. I've never busted out the stop-watch.
I like to keep apks on a2sd and put dalvik-cache on internal memory. It's kinda like raiding the two interfaces together to get the sum of the bandwidths of both when launching a program.
siberx: I'm sticking with the N1 until I find a decent phone that has been designed to fit in my pocket instead of sitting in a purse or on the bar too... I considered the glacier for a while, but, near as I can tell, the only benefits of going there are better touch screen and gpu.