We need skilled, dedicated, empowered security staff to deploy, monitor, and manage the infrastructure or the benefits of IDS will go out the window. In addition, there are too many false positives with IDSes. You need dedicated staff to filter and selectively track down the real attacks. There are too many rotten apples who would spoil it for the rest of us. On the other hand, we can't take everything that our firewalls and IDSes tell us at face value.
Many attacks are either false positives or harmless insomniacs.
Tracking down these useless leads often enough will desensitize you to the real attacks being performed right under your nose. Our industry needs to come together and determine acceptable tolerance levels and definitions for attacks. There needs to be serious discussion and legal precedence set to define what is and what is not an attack, and the people managing the technology need to follow these guidelines before expending energy. The genesis of Hacking Exposed has closely paralleled Security Watch and was driven by our continuing desire to bridge the gap between IT support and the real world of security. After many years of waiting for such a book, we finally wrote it ourselves.