fsck reports errors on clean filesystem (mounted rw)

[cronfy]

Hello.

I ran fsck on my filesystems while system was running (partitons were
mounted rw with moderate FS usage). fsck reported there were errors
(INCORRECT BLOCK COUNT and others). I decided to reboot to single mode
and check all filesystems. But in single mode fsck did not find any
errors.

 1. Can I be sure my filesystem is consistent?
 2. If fsck reports nonexistent errors (and probably will try to fix
them if asked), isn't it even danger to run fsck on running system?
 3. How can I check (not fix) filesystems while partitions are mouted
rw and are under usage?

FreeBSD 7.3/kernel, 7.2/world.

Thanks in advance.

-- 
// cronfy