How does one know if the FP got successfully filed?
I know of at least two websites where one can file flight plans, and no doubt there are more of them about.
But if one finds out that one's VFR FP has vanished only after cramming the passengers and luggage into the plane, starting up and asking for departure, that isn't an improvement.
I have lost up to 3 our of 4 flight plans filed, on one occassion. They were filed at an airfield with the proper terminal into the system. I always put my mobile number in the FP but not once has anybody called it. I am pretty sure that no attempt is made to contact the pilot if somebody in the system chooses to dump the FP. They just chuck it in the bin.
A website isn't the proper solution. It is handy but what is really needed is a means of knowing if the FP reached all its addressees.
One may as well fax the FP to the start, the destination, and the FIS stations en-route. Far more reliable...