On the one hand, the Beige Book report is a lagging indicator, in that it is a report of what already happened in the districts, not what the Fed Districts think is going to happen. On the other hand, many economists consider it a leading indicator, in that it could get the Fed to change the Fed Funds rate which is, in itself, a leading indicator.
Therefore, even though the name itself is enough to induce a yawn, the Beige Book's importance should never be underestimated when trying to gauge the health of the U.S. economy.
By the way, if you think "Beige Book" is a dull name, the real name is "Summary of Commentary on Current Economic Conditions by Federal Reserve District". See how many people know that at the next cocktail party.

