Hi there,
Price to book is but one data point - it should never be the sole data point in which one makes an investment decision. SO while it does have relevancy along with other metrics and depending on context, its not the be all and end all.
That being said, anyone investing in a company that is a going concern, should probably pay a little attention to things such as book value. If the company needs to sell itself, or sell portions of the business to improve its financial situation, then valuations certainly become important. Without context its impossible to say what is good/bad, but you'll want to see what it looks like against its own historical value.
The other metric that may have more relevance in this instance is Enterprise Value. While book value is the accounting value, EV is a more accurate reflection of the total market value of the company. It takes into account the market value of debt and equity which would be a better representation if one was looking to sell assets. In fact, its preferred over book value in many cases.
Mat