This weekend I followed the advice in this forum of looking at high growth recent IPOs for shorts. I found JIVE, a company that sells a social network designed for business workforce. I then drew a comparison between Jive and Yammer in which Jive is basically the Spotify of music while Yammer is Pandora. Yammer, like Pandora focuses on customer growth and less on charging for a product. Seems like a good LT strategy. I did some ratio comparisons (p/s, revenue growth rate) based on CRM and LNKD after their ipo and Jive was pretty overvalued. So Monday morning I put in my short position on IB and turns out its not shortable 
I also analyzed another company and was able to short at a good price, JAZZ (biotech). Right now it’s working but I’ve done a couple valuations of fy 2013 earnings and 2013 p/fcf and its trading around comparable fair values. My reason for shorting JAZZ is they are experiencing changes in capital structure, operating margins, and lawsuits that can damage future revenue growth. Around 60%-85% of their revenues comes from selling a medicine for narcoleptics. Their monopoly patent for this drug expires in November and one company has filed for a cheaper generic version. In addition, they are facing potential consequences from the FDA for failing to complete proper protocol on documenting reports of adverse side effects and deaths. Their product has been compared to GHB due to its chemical structure and effects. Failing to disclose negative reports about a product synonymous with GHB seems consequential. And finally, they have raised the price of this product every 6 months since 2008 and it costs about $50,000 a year if you take the average recommended dose nightly. That is a disgusting drain on medical insurance companies and a cheaper generic version would drastically lower their sales price.
Unfortunately, the downside to shorting is they have solid revenue growth and good margins. They still have significant growth possibilities and the ability to bring in 20-30% net profit margins. But patent and fda lawsuits might make 50-60% of revenue move downward. In conclusion, this company seems very sleezy–shareholder dilution, debt financed inorganic growth, continuously raising prices on their monopoly and possibly ignoring reports to avoid intervention.
---------Questions:
What are the best ratios and metrics to use in order to derive an intrinsic value for these two companies? For JIVE, all that seemed applicable is P/S. They are trying to be a momentum growth stock, but they have no earnings, long term history or competitor with similar market cap. For companies like these (LNKD, GRPN,P) is it better to just use a DCF valuation where you imply high revenue growth and improving operating margins each year?
And for a profitable biotech like JAZZ, is it more appropriate to use a comparable ratio analysis for similar biotechs with high gross margins? Which one do I use, P/FCFF ?? 
I know there is no absolute answer, but I just want to make sure I take my stories down the most objective path.