I have tried to over pitch into lagers, and have not been able to do so. I have put 4 to 5 times the recommened amount from Mr Malty... and had no ill effects with lagers. (my method was to brew three batches of the same recipe in series, using the yeast cake for the next. Measured in a beaker... and dumped in the next. I was looking to find out how much was too much, but when I hit over 4x the first batch... and there were no differences we could make out... I figured that was enough)
However, you can certainly under pitch. If you go half of what Mr Malty says, I think the lagers come out with noticeable differences. (fruitier/ale like, more sulfur, and took longer to clear)