I use it, but the one time I attempted to access it from my cell phone to open my flight plan, I got bit. I had filed my VFR flight plan earlier. Once in the air, I accessed the web site and opened my flight plan just fine, but there was apparently no option to set the time I had taken off, which was about 29 minutes later than estimated on the flight plan I had filed. Thus, I landed at my destination 29 minutes "late" and was 31 minutes "overdue" when I emerged from the men's room at the FBO and tried to close the flight plan. Online, I could not even access it, so I called in and was told that I could not close it because it had been sent to S&R due to my lateness. So it seems like the best option is to file from the website but open your flight plan over the radio.
Leaving that aside, I use the briefing features for every cross-country flight. I get an outlook briefing and then schedule an e-mailed standard briefing for maybe an hour before I need to decide between flying and alternatives.
