About ext2 filesystem creation
 

When i create an ext? filesystem using mke2fs, it reserves 5% space! for super user when run with the default settings. What exactly is this space used for? Anything very important? Am i doing anything terribly wrong by giving '-m 0' option?

It provides a way for root to access (log in) in case the file system free space is 0%. With the file system full a regular user will not be able to log in because there isn't space to create tmp files etc. It is also supposed to keep fragmentation down.

I do not see the need for reserved space on data partitions but I would keep a min 1% on /, /home, /var just in case.