hey, i'm new here, but i've been riding a fixed gear for a few years now. i don't know much about bike mechanics, but i'm trying to learn b/c i'm sick of people doing half-assed repairs on my bike.
i'm sure i'll have way more questions than this as i learn, but here are a couple:

1) i had my bike worked on recently and now it's unbalanced. i used to be able to ride no handed with almost no effort, now i have to compensate for my bike's imbalance with my body while i ride, which is really annoying. what could cause this?

2) i was looking at the fixed gear gallery site and i notice a lot of people have these things on their dropouts that look like they help set the back wheel/pull the chain tight. i'd love to get a set of these, b/c setting my back wheel has been a sort of voodoo practice for me, and i want it to be more precise. what are those called?

thanks for your help,
-et-