Trying recovery with wipe/data factory reset option results in
E:format_volume: make_extf4fs failed on /dev/block/platform/s3c-sdhci.0/by-name/user-data
It sounds like there are 2 different causes for the Nexus S boot problems discussed here:
1. Filesystem corruption (occurs with low battery shutdowns?)
2. Hardware issue with a BGA component that Samsung is willing (under what conditions?) to replace. Is Samsung replacing the flash memory due to failing/poor solder (this would explain intermittent startup issues)?