[Updated 11/4/2013] Gmail has patched this bug.
Please note we have discovered a technical problem with Gmail which is flagging certain emails containing the word “lolz” as unsafe email meaning it will never arrive in your inbox or even your spam folder. This lolz problem had an effect on some PMs sent between our members.
For the time being and until this bug is fixed by Gmail staff, we will rewrite “lolz” to “lol” in our alert emails. Keep in mind this “lolz” issue is widespread based on our internal tests and for the time being we advise everyone to avoid using the word “lolz” in their future emails to gmail users.
You can test this yourself by sending an email containing the word “lolz” in the email body to a friend with a gmail account. Hopefully this bug will be fixed by Gmail soon.