You could argue that marconi (to name one) was undervalued in the eyes of those that bought it or else they would not have bought it.
Your value for a share is what you are prepared to pay for it. It will be different 'value' for many others. If it wasn't different we would not have a market
I traded CW today and every upside move was sold into. This tells me that someone is probably dumping a lot of stock. It may bounce from the 80p level as it seems to have found some support here but I am sure a lot of Marconi holders had the same thought at various stages of its fall. Not that I am saying that C+W is in the same boat as marconi, just using it as an example of how quickly a 'good value' stock can fall.
I am long overnight with a spreadbet on this and Corus but will close both pretty sharpish tomorrow if:
a. they put on any sort of reasonable gain, 5-6p for CW and 3-4p for Corus.
b. The Dow tanks tonight especially if any decline is led by tech stocks
c. they hit my stop in the morning
My preference would be not to have held either overnight but I have decided that if these do open with any strength then they could be nice gainers and that a large part of the downside has probably been taken out of them today. Also I had not hit my breakeven when the market closed and the Dow seemed to have a fair amount of strength following the Greenspan moment of light ;-)
The problem with bottom fishing after a large drop is that it takes time for the news to get out to the private investors. It is 50/50 which way these go tomorrow.
Any gains now it has moved against you should be seen as a bonus. Don't hang around waiting for it to hit your entry price. If it is weak tomorrow than get rid of it.
PS. none of the above opinions should be construed as advice to sell or buy any financial instrument. They are merely my own views.