Hi,
I've formated my MicroSD card with ext3 to get permission and symlink/hardlink support but the card isn't mounted automatically while booting.
Do I have to anything to get it mounted?

As root:

Eh, you shouldn't need to manually mount it. I formatted a couple cards as ext3 as an experiment and everything worked flawlessly for automount.

My own SD card is formatted ext2 and it has never automounted at boot. I always get "partition format not supported" message during boot. Is it that ext3 is supported and ext2 not?

I only put podcasts on that partition and do not want the extra overhead, wear, and slower performance of a journaled file system.

ext3 is just an extended ext2 (added journaling).

Yes. So? ...

so when ext3 works... ext2 should work as well ^^

I agree, quite strongly. It seems really odd that ext3 would automount and ext2 not. But that is exactly what happens for me. I had been assuming that ext3 also would not work.

If someone has a microSD card with only a single ext2 partition that automounts on the n900, please let me know.

This is a little less surprising because of what has been learned about the camera application. Everyone thought that it would only write to a VFAT partition. It turns out that it creates the DCIM directory owned by root and VFAT does not have owner attribute and extN does, so the camera application can not write to the DCIM directory on a regular partition unless it has permissions 777 or owned by user:users.

http://talk.maemo.org/showthread.php?t=35122&page=14

Automount doesn't work for me, I just tested it again.
I've taken a look into the fstab and there is also no entry for the card and because this file is generated every boot again it doesn't matter if I add the entry myself.

Did you change the partition type of the microSD to be type 83 (used for Linux partitions) or did you leave it as a FAT partition type and just change the format of the file system on that microSD partition?