Most successful Darkwraiths will have 99 on their characters; it doesn't take long, maybe a few hours to get a decent stack on your counter if you mostly win. It's a huge defense bonus at low levels so there's a big incentive. It doesn't really take too long to farm stacks of humanity with the dlc either, some players go that route.
Chikubi ga itai. Hontou ni- Mattaku kayuku itai. Bakuzen to aamondo to niru...
I don't have 99 humanity anymore on my low lv character. Lost it all farming titanite chucks and slabs in new Londo. Took a wrong turn over an edge with a long drop while going for my stain. Guess its karma for my part in invading in the parish. The thing is if it was karma for that it didn't work because now I have to go back to invading for more humanity. Circle of life I guess.
After a couple hours of invading and PvP i'll get 99. Isn't really worth anything to me so i'll usually join another covenant to get something cool, then rejoin the darkwraiths so I can continue to give humanity. I don't need it, but I also despise losing large quantities of souls/humanity even if I never use it.