Today, my backup has been verified (TimeCapsule-based) as part of the monthly "schedule".
So it seems that the issue is located on non-TimeCapsule drives, at least in my case.
On another side, my index is toasted:
3/13/12 8:33:31.610 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:34:32.771 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:35:34.394 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:36:34.881 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:37:35.994 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:38:36.795 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:39:37.611 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:40:39.220 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:41:39.614 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:42:39.768 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:43:40.714 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:44:41.550 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:45:42.372 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:46:43.854 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:47:45.391 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:48:46.764 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:49:47.053 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:50:48.668 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:51:49.289 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:52:51.179 AM com.apple.backupd: Waiting for index to be ready (100)
3/13/12 8:53:51.658 AM com.apple.backupd: Waiting for index to be ready (100)
Raf