this one's good:
http://l33t.spod.org/ratx/DS/dslazy/
the thing about the modified firmware is that you can restore it or reflash it at any time if anything goes wrong. With the original nintendo DS firmware.. you're not allowed to touch it.. you have no access to it.. so if its bricked its bricked

What prevents you from reflashing it? well.. you can't boot it up at all. I *believe* the alternate firmware, if you hold down a certain button combination when you turn on your DS, will start the restore process. I could be wrong.. but I know for a fact that there is a restore option built into the Flashme firmware.
A lot of people flash their DS if they have friends who also want to buy flash carts and want to save the $20-30 on the Superkey/Passcard. I personally didn't flash mine until recently, only because a friend of mine wanted to buy my Passcard and paid me more than what I paid for it

. Flashing takes like 5 seconds literally.. when I first did it I thought to myself "thats it?"