One of the advantages of LiFePO batteries is that the self discharge rate is extremely low - I've been told around 10%/year, vs around 10%/month for a typical lead acid. They also have significantly lower internal resistance, allowing a battery with a much lower capacity for low-rate discharge to act like a bigger battery for starting a bike. A LiFePO battery with a 14Ah EQ rating will only put out around 1/3 of that if it's a slow draw, but it'll start a bike just as well as a 14Ah lead acid. That means that they're very light (duh) but also more susceptible to parasitic drains, but if you don't have any, you can let the bike sit approximately forever and it should still crank hard.
2004 625SMC STOLEN 9/18/2009
2006 SV1000, not stock
2003 WR450F supermoto - street legal, Excel/Talon wheels, Brembo/Braking brakes, etc
2002 YZ426F/448 supermoto - Behr/Talon wheels, Brembo/Braking brakes, etc