Lost .ssh known_hosts (AGAIN)

for the second time in 2 wks my known_host file has diapered from existence and before I restore it from a back up I would like to ask if anyone knows why this may be?

I'm not sure how to explain it other than it's just gone, (really blank) and I would have to re upload my id again to all my ssh sites and this worries me a bit.

I also lost all my saved passwords (on or about this same time) so I had to repopulate those as well (I'm not sure what file I need to back those up. haven't really looked to be honest with ya, but that is on my todo list.

all this being said I started poking around and discovered that I trust a TON of sites that may or may not need to be there...

I don't like trusting anyone so much as to give them a certificate space on my box.
I started deleting some of them with out noticeable side effects. I assume they are ssl cert that can't do much other then say that this site is the site it says it is.
or am I way off on this?

Thanks for any help on this