Not really. For many high-tech companies, the earnings can vary a lot from one quarter/year to the next. If the profit margin is hovering in the +/-10% range, the P/E can vary wildly. Even in a low-earnings period, wall street will typically not punish the company too much if it expects things to turn around soon.

Regarding Salesforce.com in particular, looks like its 2006 profit margin was 9%, but 2007's was 0.1%. The street is still optimistic though, because the company's revenues increased 60%.

For such companies, the P/S ratio is generally a more reliable metric to compare with. Salesforce.com's P/S ratio is 8.8. For reference, Google's is 13.