Sometimes (ok,rather often) unfold doesn't give you the best unwrapping of a chart, sometimes the chart needs more cuts to be able unfold nicely, but sometimes the cuts should be enough to get a decent unwrapping.
You can give the unfold algorithm a helping hand, you can give more input by selecting some vertices in uv window and re-run the unfold command from the vertex menu.
For example, you have modeled a head with virtual mirror on, you want the mirror edges to form a straigth line on the uvmap as well, then select all vertices in the chart that belongs to the mirror edges, make them straigth by for example using the flatten command, and re-run the unfold command.
I got another example of an hand that unfolded horribly by autouv, only the top faces where used as a chart.
As you can this unfolding wasn't greatest, the three leftmost fingers are supposed to be about the same size, and the thumb (to the right) should be smaller but not that small.
I try to improve it by moving the top vertices on the fingers, so that I get the correct lengths of the fingers. I.e. to match the model all fingers should be about the same length, except the thumb. I also keep fingers apart so we give up space for all faces on the fingers.
Then I select the vertices that I want autouv to keep (selected in the image above), the rest will be calculated. Here I want the top vertices of the fingers to stay, so that we get the desired fingers lengths.
Invoke unfold again.
And the result is alot better.
