Snowy,
Most techniques I've seen recently don't use magnetic lasso, but rather rely on differences in contrast to make selections. Split the image into its RGB components, and look at each Component layer to see which one's contrast best isolates the features you want to keep or change. Make the selection using selection brush or lasso in one component layer, then go back to 'combined RGB' mode and proceed.
You might take a look at
http://graphicssoft.about.com/od/pho...bps_5agirl.htm It gives an example in PS of isolating a subject with wispy hair.
I recall years ago seeing a writeup in POp Photo on a software plugin that handled halo-less selections of difficult subjects, but I don't recall the product name. Perhaps someone else knows the name of currently available products that work that magic.
I'll be interested in seeing all the other responses you get to your question.