I can't really fault AFPEx if you are sitting in front of a PC on ADSL, or you are travelling with a laptop and have a 3G connection. I like the simplicity and immediacy of filling in the flight plan form and getting an ACK (or a REJ) within seconds. Anybody who can use a website or a bit of software on a PC can use it (if shown how).
In all other situations the system can screw you.
The need for a fast connection is not because it needs one for normal operation - it is caused by the server occassionally insisting on downloading the whole application, and this event is totally unpredictable. I normally work around it by not closing the application and using Hibernation to shut down the laptop, but sometimes a reboot is required due to something else (e.g. installing or removing some software) and then you better be on a good connection to reload the application.
A lot of the time, the need to delay a flight plan becomes apparent while one is e.g. driving, or on a train, etc.
I think a long term solution to all this will be an SMS service because that is the only cost effective means of doing this H24, and it will come, but not from AFPEx who bought an off the shelf program (from Comsoft in Germany) and have to pay dearly for any changes to it. And since some 99% of GA doesn't pay....
AFPEx did delay flight plans for me in the past, and they also did stuff like retrieving and re-filing a flight plan which I filed with the wrong DOF. All done instantly and cheerfully. I suspect they have recently had some "staff cost accounting" issues and, given the heavily political nature of the system which is privatised but still mandated to deliver certain specified services, have probably decided to chop a few things off around the edges.