During our security training we found an interesting forum entry (CPU Oct 2006 Problem) in Oracle Metalink. It seems that a portscan with nmap on AIX 5.2, OAS 10.1.2.0.2 CPUOCT06 causes a denial of service problem on port 443 (HTTPS). It’s not clear if this problem affects all platforms because nobody answered the forum entry.
Normally it is a good idea to apply CPUs as soon but sometimes new bugs are introduced. Often these problems are specific to a special platform. Another example of a bug which was introduced by the CPUOct2006, CPUJan2007 and CPUApr2007 was a rman problem on Windows 32 bit (Rman fails to restore in 188.8.131.52 with CPU patch installed on Windows platform).
Before applying a patch on a production system you should always perform tests.