I have bro version 0.9a6 running. I see impressive sizes for files in /usr/local/bro/logs.
For example...
[rreitz@gumshoe rreitz]$ ls -l /usr/local/bro/logs/*04-10-03*
-rw-r--r-- 1 bro wheel 88835 Oct 4 00:00 /usr/local/bro/logs/alarm.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 787345802 Oct 4 00:00 /usr/local/bro/logs/conn.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 3337706 Oct 4 00:00 /usr/local/bro/logs/ftp.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 4008666 Oct 4 00:00 /usr/local/bro/logs/http.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 28576 Oct 4 00:00 /usr/local/bro/logs/info.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 139345 Oct 4 00:00 /usr/local/bro/logs/notice.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 236 Oct 4 00:00 /usr/local/bro/logs/signatures.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 14411249 Oct 4 00:00 /usr/local/bro/logs/smtp.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 531 Oct 4 00:00 /usr/local/bro/logs/software.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 59967793 Oct 4 00:00 /usr/local/bro/logs/weird.gumshoe.04-10-03_00.00.00
-rw-r--r-- 1 bro wheel 0 Oct 3 00:00 /usr/local/bro/logs/worm.gumshoe.04-10-03_00.00.00
but the reports generated for 10/3 are empty.
[rreitz@gumshoe rreitz]$ ls -lt /usr/local/bro/reports/local/
total 26
-rw-r--r-- 1 root wheel 1499 Oct 3 00:43 FNAL.1096781400.60653.rpt
-rw-r--r-- 1 root wheel 1499 Oct 2 00:42 FNAL.1096695000.56628.rpt
-rw-r--r-- 1 root wheel 1499 Oct 1 00:40 FNAL.1096608601.53259.rpt
...
The report size of 1499 contains header/footer formatting only. For example...
Site Report for FNAL, from 2004/10/02 00:30:00 to 2004/10/03 00:30:00
generated on Sun Oct 3 00:43:37 2004