The #1 problem is that you are shooting DV, which is notoriously difficult to key. the #2 problem is that since DV is so unforgiving, your lighting of the greenscreen itself needs to be spot on, or no amount of post production tweaking will save your shot. The lighting on your actor is important, but nowhere near as important as the lighting on the screen itself since this dictates how much pushing and pulling you will need to do in your keyer app to remove the backdrop, and all that pushing and pulling ultimately degrades the quality of your edges. I typically light my screen with two KinoFlo fluorescent light banks and a 2,000watt Arri light bounced off of a white card on the floor just below or above the screen. here's a still from a shoot I did last week that, when using the high res source footage, practially keyed itself even though we were only using DVCPRO 50, one small step up from DV:
Your greenscreen should register 50-60 IRE on a waveform monitor (in the image above it is about 53 IRE, I prefer 60). If you don't have a waveform available (who does), another option is to shoot a quick test clip on set and pull it into Final Cut Pro (maybe on a laptop), which has a reasonably accurate waveform built in.
Also, the lighting must be PAINFULLY even. Variations that are barely noticeable to the naked eye will cause you to push the keyer much harder just to get rid of the entire backdrop. This will cause your edges to get uglier and uglier, from which there is no pleasant workaround.
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In answer to your actual question (tangent? Who, me?) here's a few steps to try that should help your keying:
1. Precompose your greenscreen footage. Within this new comp, create an adjustment layer above the footage, and apply the "Median" effect (Effects > Channel > Median). There is only one value to play with, change it to 3 or so. Put the layer in "Color" blending mode. Now apply Keylight to the composition itself (you will need to nest it within another comp), NOT the source footage. Right off the bat, this will help a LOT of your edge problems.
2. Do not apply any color correction to your plate before doing the greenscreen extraction. Many people try to "cheat" the keyer by boosting values before they key, but it will NOT work and will make your key worse.
3. Break your key up into zones if needed, as this is how the pros do it on feature films. To retain fine hair detail you typically need much more delicate settings than are needed to remove the fringe around sleeves or pants, and one keyer setting applied to both will force you to compromise the quality of both. Duplicate the footage for each area that will need its own treatment, using masks to separate out each element. This way you have one layer that is just the head, one layer for the clothing etc. Then apply different keyer settings to each layer to suit its needs. You will need to animate these masks (depending on what happens in your shots) but again, this is how the pros do it and if you want the best results, this is a good place to start.
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