I changed my driver's side sensor at the manifold very recently. It really wasn't that bad. I used the small O2 sensor wrench in the Autozone loaner kit. It probably wasn't necessary on my car, but I sprayed it with a mix of acetone/ATF to help break it loose.
The sensor was easy, but the thing that took the longest was experimenting trying to put pressure on the tab of the electrical connector. I ended up using a very small flat-blade screwdriver clamped into some needle-nose vise grips.