I had a problem (way back in April 2007) on a 4 node RAC. I spread out the alert logs from the 4 instances in front of me and tried to see a timing correlation across the nodes. So, "X" occured at 12:54:13 on NodeA, what happened at NodeB; so I search (with my editor) for a "close" timestamp in the other alert file... this was tedious!! So I wrote a quick program to try and do this automtically. A text browse of the alert file(s) with an automtic implict search of the timestamps.
The program is freely available (no guarantee, your milage may vary, professional driver on a closed course, do not wash, mangle or wring, not valid about 5600ft, etc and so forth) here at the oaktable site.