Thanks for the responses, they were very helpful. jtbandes gave me the first step in solving the issue, but I wanted to go into detail of the other parts in case it helps others.
I was able to get the problem to happen in a reasonably reproducible way with Adium. Basically, start the app up, open a conversation, type in some text and then right click on some of the text. Spinner the first time after launch, lasting for over a minute.
So I started up Spin Control, went into the preferences to target only Adium, followed the procedures to cause the problem. Was able to get a text report of the issue and found what I expected was the issue:
5531 -[NSApplication run]
5531 -[NSApplication sendEvent:]
5531 -[NSWindow sendEvent:]
5531 -[NSTextView rightMouseDown:]
5531 -[NSView rightMouseDown:]
5531 -[NSMenu _popUpMenuWithEvent:forView:]
5531 -[NSMenu _popUpContextMenu:withEvent:forView:]
5531 -[NSMenu _popUpContextMenu:withEvent:forView:withFont:]
5531 -[NSCarbonMenuImpl _popUpContextMenu:withEvent:forView:withFont:]
5531 ContextualMenuInsertItems(MenuData*, unsigned short, AEDesc const*, ContextualMenuHelp const*, unsigned long*, OpaqueContextualMenuItemsRef**)
5531 TContextualMenuPlugin::LoadContextualMenuPlugins(FSRef const&, __CFArray*)
5531 TContextualMenuPlugin::LoadCMPluginsFromCFPlugin(FSRef const&, __CFArray*)
So it did appear that I was running into an issue with a plugin, but the context lacked for details of which.
So I relaunched Adium but this time I also had the Activity Monitor open and selected the process and used Inspect->Open Files and Ports to monitor what specifically the app was working with. When I repeated the steps to generate the problem, I was able to grab the following from the listing (note new files/ports opened appear at the end of the list, so it is easiest to find the problem by looking at the end of the list):
/Users/tim/Library/Contextual Menu Items
From this I was able to go through the items in my local Context Menu Items directory and determine the one causing the problem.
Thanks for the help.