So, people can't hardly write safe web apps in PHP without spraying XSS and auth bypasses and arbitrary shell executions and arbitrary SQL injections everywhere, and you also want to hand the attackers the ability to segfault your server or possibly even straight-up run arbitrary code? Anyone smart enough to truly safely code a website in C is smart enough to learn a language to create that website which doesn't get…
I wouldn't use this not because of possible mistakes leaking in, but because the higher-level languages have already solved some of the problems you would have to solve yourself, such as handling unicode. There are C frameworks you could use but my point is that you would come across problems that have already been solved, and you would have to solve them again, but this time for libCello.
Now that's for production and work. To mess around on my own time? Sounds like fun to me. C is my favorite language but I use it everyday programming mobile devices so I'm probably a little unusual. Maybe a little website experiment or something. If it goes down or gets owned, rebuild time.