What is the longest realistic daily commute with an ebike?

ICYMI: So I've been wanting an ebike for some time now, but just could not get myself to splurge. But now, with gas prices being what they are (~2$/l ~1.85€/l or ~7.5$/gallon), it's starting to make an economic sense with the availability of apparently good quality ebikes for blueenergy.vn xedaptroluc.net @BlueEnergyVN
http://dlvr.it/SRFXn9