Can I symlink /data? I have a rooted Google/HTC Nexus One running Android 4.0, Cyanogenmod, and MIUI. These mods were done by the previous owner.

Considering that the amount of internal storage my phone has is really tiny, I'm always looking for ways to free up space. My current idea is to symlink either all or part of /data to somewhere on the SD card where I have lots of free space.

My question is, would this cause any problems? I've got a lot of Linux experience, but I'm an Android newbie. The filesystem seems to be a bit different from what I'm used to in the Linux world.

Also, are there any pitfalls I should be aware of, such as certain data that must be available before the SD card is mounted?
Yes you can do that. Scripts like data2sd do exactly that.