Yup. I'm one of them. The Shorai had SIGNIFICANT voltage drop when cranking my 2009 GL1800 Goldwing at temps below 40F. The voltage drop was significant enough that although the bike did slowly crank and start, the Navigation screen remained off (a symptom of low starting voltage). That is not acceptable cold weather performance.
At temps approaching 30F, the bike would not crank over quick enough to start. That is after "warming" the battery by burning the headlights for a few minutes. I even cranked my heated gear a bit to really put some pull on the battery. No improvement. Glad I was at home. I just took the truck to work.
Perhaps for smaller motors requiring less power to start (and less sensitive to voltage drop), these lithium iron batteries perform fine in cold temps. Maybe over the last year, Shorai has significantly improved their performance in cold weather (I'm skeptical). Don't use it on a Wing if you ride in temps below 50F.
For a vehicle that pulls a small voltage while sitting dormant and where 15lbs of weight loss is insignificant to the performance of the vehicle, I see zero advantage to using a lithium iron battery.
Now I do have a lithium iron battery sitting outside (sans charger) hooked up to my Yamaha stand-by generator. The ability for the battery to sit unattended for 6+ months without loosing any charge is fantastic for that application. I don't have to worry about keeping the battery "tended".
Not too unproven. Several folks I know of who had the Shorai could not start their bikes in below freezing conditions.