You don't always necessarily get banned permanently, or banned at all. Google might just discount all the links they find to be bought and adjust your ranking according to your new link count minus the paid links. You can always clean up the links yourself and then submit a reconsideration request. Whether that request is accepted, that's up to Google.
True but some times you do get a big slap BMW is probably the best known. And getting back can be a problem for sites with out a high profile and for ever after your on Googles watch list :-)
