Depends on the source of the biodiesel. If it's a result of growing soy beans or some other organic oil source just for biodiesel, it's not an energy saver.
Not true (although there are other issues involved). While corn-based ethanol barely justifies the energy use (for every unit of energy used to produce it, 1.2-1.8 units are created), plant-based biodiesel is a lot more efficient with an energy return ratio of 3.2. Also, since growing the source crop captures CO2, biodiesel is almost carbon neutral (almost, because 10% of raw input is methanol).
The other issues include the very real problems of replacement of food crop acreage with fuel crop acreage, and energy used to work the fields. This varies with the type of crop.
Disclaimer: I'm an investor in and a staff member of San Juan BioEnergy
which is a biodiesel startup in Dove Creek, Colorado. We have just begun building our plant, which will crush locally grown sunflower seeds into oil; the majority of this will be sold as food oil, but some of it, along with recaptured cooking oil, will be made into biodiesel. Sunflowers grow well in this high desert without irrigation or other intensive farming practices, and are a good rotation crop for wheat and beans, which are the traditional crops grown here in SW Colorado.
I would be happy to answer questions or discuss biodiesel! In fact, we bought a diesel-engine Sportsmobile (last week :-) with an eye to running off biodiesel - figure we'll put our money where our mouth is, so to speak.