Hello

Right, I'll take all the flames I deserve for this, as I've done the unimaginable! All right, I'm a coy boy, I know it now.

Instead of reformatting /dev/sda I reformatted /dev/sdb, and lost all the data that means anything to me.

In short, /dev/sdb3 was a 200gb reiserfs partition, and using YASTs partioning tool, I created and formatted /dev/sdb3 as a 50 GB fat partition, and the rest of it (sdb4) as reiserfs.

I'm holding onto a thin hope that I may be able to get the data back? Either on my own if possible, but if I can't, I've heard it can be done commercially..

I am being way too optimistic?

there are all sorts of guides about for this e.g http://www.unixwiz.net/techtips/recovering-ext2.html .essentially you need to recreate the partition table as you had it, so that the partition boundaries match up. once you have the correct boundaries you can try mounting the partition directly, and in an ideal world this could work. few worlds are ideal though, other tricks to try would involve using a tool like parted to scan your disk for spare superblocks for your partition and mount it using different blcoks if the main one is corrupted. Also i believe that parted is also good for finding probable partition boundaries too, but as nothign is set in stone you need to understand a fair bit about what you are looking at, as parted can only guess and look for typical patterns etc.