Okay, I dist-upgraded a few minutes ago, allowed guest acces (using nautilus) and could connect to the share. I tried some Visual Studio compilations and crash message appears in the log file.

I paste a crashdump from karmic:

  alloc_sub_basic: NULL source string!  This should not happen
[2009/09/04 09:13:02,  0] lib/fault.c:41(fault_report)
  ===============================================================
[2009/09/04 09:13:02,  0] lib/fault.c:42(fault_report)
  INTERNAL ERROR: Signal 11 in pid 3015 (3.4.0)
  Please read the Trouble-Shooting section of the Samba3-HOWTO
[2009/09/04 09:13:02,  0] lib/fault.c:44(fault_report)
  
  From: http://www.samba.org/samba/docs/Samba3-HOWTO.pdf
[2009/09/04 09:13:02,  0] lib/fault.c:45(fault_report)
  ===============================================================
[2009/09/04 09:13:02,  0] lib/util.c:1480(smb_panic)
  PANIC (pid 3015): internal error
[2009/09/04 09:13:02,  0] lib/util.c:1584(log_stack_trace)
  BACKTRACE: 20 stack frames:
   #0 /usr/sbin/smbd(log_stack_trace+0x2d) [0x703ecd]
   #1 /usr/sbin/smbd(smb_panic+0x2d) [0x703fed]
   #2 /usr/sbin/smbd [0x6f192e]
   #3 [0x12f400]
   #4 /usr/sbin/smbd(str_checksum+0xd) [0x7012bd]
   #5 /usr/sbin/smbd [0x4dae2c]
   #6 /usr/sbin/smbd [0x4e738b]
   #7 /usr/sbin/smbd(reply_trans2+0x706) [0x4e8956]
   #8 /usr/sbin/smbd [0x50c89e]
   #9 /usr/sbin/smbd [0x50cd1d]
   #10 /usr/sbin/smbd [0x50d520]
   #11 /usr/sbin/smbd(run_events+0x12e) [0x7152de]
   #12 /usr/sbin/smbd(smbd_process+0x7b9) [0x50c129]
   #13 /usr/sbin/smbd [0x9e4918]
   #14 /usr/sbin/smbd(run_events+0x12e) [0x7152de]
   #15 /usr/sbin/smbd [0x71557f]
   #16 /usr/sbin/smbd(_tevent_loop_once+0x79) [0x715b79]
   #17 /usr/sbin/smbd(main+0xc88) [0x9e5638]
   #18 /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe6) [0xb7f77b56]
   #19 /usr/sbin/smbd [0x487ac1]
[2009/09/04 09:13:02,  0] lib/util.c:1485(smb_panic)
  smb_panic(): calling panic action [/usr/share/samba/panic-action 3015]
[2009/09/04 09:13:02,  0] lib/util.c:1493(smb_panic)
  smb_panic(): action returned status 0
[2009/09/04 09:13:02,  0] lib/fault.c:321(dump_core)
  dumping core in /var/log/samba/cores/smbd
[2009/09/04 09:13:02,  1] smbd/service.c:1043(make_connection_snum)
  w004d038 (::ffff:148.198.114.89) connect to service foo initially as user nobody (uid=65534, gid=65534) (pid 3030)
[2009/09/04 09:13:06,  0] param/loadparm.c:8541(process_usershare_file)
  process_usershare_file: stat of /var/lib/samba/usershares/foo failed. Permission denied
[2009/09/04 09:13:07,  0] lib/substitute.c:560(alloc_sub_basic)
  alloc_sub_basic: NULL source string!  This should not happen
[2009/09/04 09:13:07,  0] lib/substitute.c:560(alloc_sub_basic)
  alloc_sub_basic: NULL source string!  This should not happen
[2009/09/04 09:13:11,  0] param/loadparm.c:8541(process_usershare_file)
  process_usershare_file: stat of /var/lib/samba/usershares/.git failed. Permission denied
[2009/09/04 09:13:11,  0] param/loadparm.c:8541(process_usershare_file)
  process_usershare_file: stat of /var/lib/samba/usershares/.git failed. No such file or directory
[2009/09/04 09:13:11,  0] smbd/service.c:1184(make_connection)
  w004d038 (::ffff:148.198.114.89) couldn't find service .git
[2009/09/04 09:13:12,  0] lib/substitute.c:560(alloc_sub_basic)
  alloc_sub_basic: NULL source string!  This should not happen
[2009/09/04 09:13:12,  0] lib/substitute.c:560(alloc_sub_basic)
  alloc_sub_basic: NULL source string!  This should not happen
[2009/09/04 09:13:12,  0] lib/fault.c:41(fault_report)