Saw this error on 0.7.1rc1 after running bitcoind in screen for approximately 48 hours off an encrypted home directory:
EXCEPTION: N5boost16exception_detail10clone_implINS0_19error_info_injectorINS_10filesystem22basic_filesystem_errorINS3_10basic_pathISsNS3_11path_traitsEEEEEEEEE boost::filesystem::space: No such file or directory: "/home/user/.bitcoin" bitcoin in ProcessMessages()
Machine info:
Linux hostname 3.2.0-26-generic #41-Ubuntu SMP Thu Jun 14 17:49:24 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
I will see if I can recreate this and provide more useful information. User and host info was anonymized.