I have sold both MDCO and CELG, because they broke down and activated my stop-loss orders. I never regret selling stocks that go down, no matter how I like them, if they sink on the stop-loss level, they're out. I won't probably look at the again, unless they bounce back significantly and make new highs. Both are good stocks but their trends might be over.
A big disappointment was Blinkx (BLNX.L), which slumped 21% on an article by a Harvard Professor, Benjamin Edelman, who questioned it's sources of revenue. He looks like an expert on this subject (although he has paid to write the article and refuses to reveal the identity of the buyer), and I have missed some things in my analysis, as the company might be using shady ad tactics to get traffic and extract money from advertisers. I'm not so sure if I would be able to discover such things even if I went into checked every detail in it's financial statements. My understanding of their business was not as deep as I thought. My stop loss got hit around 136, so I lost nearly 19% on a stock, which showed me a gain of 30% just two months ago. Too bad, but as they say, shit happens. For situations like this, I have stop losses and other stocks to diversify and limit a loss to my entire portfolio. Nevertheless, the UK Value/Growth portfolio got hit pretty hard, it's now up only 11% from November, down from 20% in January but still much better than -4.65% for the FTSE100.