The stock BIOS that ships with the Asus 1215N is a fine BIOS... for a stock system. Unfortunately, it doesn't allow access to more than 2.8GB worth of RAM. As most people upgrade their systems, this is a bit of a downer - adding another 2GB for only 800MB more usable is no good.
Fortunately, updating the BIOS is easy - once you know the trick. Remember all that "Create a DOS boot CD, run the flasher" rubbish? No more! The Asus EZ-Flash system lets you flash directly from a USB stick (or, possibly, other media - but as the 1215N only has a USB port, it's the one we're using).
The trick is that if you try it, it probably won't work.
Why? EZ-Flash seems to require a hideous FAT16 filesystem to function. It also seems to require that the ROM be named "1215N.ROM" (for unknown reasons possibly related to old junk on my USB key). If this is enough for you to succeed, awesome, otherwise read on...
Creating a FAT16 filesystem is relatively easy under Windows.
This WILL blow away any old data on your USB key. This should be obvious...
Delete the partitions, create a new one (or just use the RAW partition - this works too), and then create a "FAT" filesystem. Not a FAT32 filesystem - just FAT.
Copy the ROM from the Asus download site to the USB key as "1215N.ROM" and then reboot with the USB stick in.
After rebooting, in the BIOS, press Alt-F2 repeatedly. The system should recognize the USB key and flash the BIOS, opening up your full amount of RAM!
From what I hear, the system can support 8GB, but I think 8GB in a netbook starts to get into "Wait... what?" category. However, it might be worth trying if you're doing something RAM-heavy and CPU-light...