Well, I run pure B100 and I'm very satisfied doing so. Here's what I found out in 2 years on my 240D and my 300D as well as my Dodge Ram 4X4.
Pro's
1. Biodiesel runs much cleaner and I get through emissions with no problems!
2. Mercedes Benz and Cummins did a study from 1994 to 2000 comparing Biodiesel and concluded that it helps reduce operating costs because it is not as corrosive, it runs cleaner and after 6 years of metal particulate tests, it would not be unusual to be able to get twice the engine life from Biodiesel vs. Fossil fuels!
3. I do not have to wait in line for fuel and when I go to Western States Petroleum, I get enough to carry me through for a week or longer and just pump from my house.
4. The engine runs a lot quieter and with much less smoke.
5. The exhaust smells like food cooking! (It's amazing how many appetites I stimulate with both cars!)
6. If you spill some on the ground, it will not poison the soil. (Millweeds however love it, it will not kill them. In fact they grow taller and bloom more profusely, so if you have millweeds you want to get rid of pouring Biodiesel on them to kill them won't work!)
7. We spend the money on fuel here instead of sending it to other countries that don't like us. (Feed a farmer, starve a terrorist!)
8. You help the U.S. achieve alternative energy independence while helping out National Security at the same time.

Now the Con's
1. Your actual horse power or engine kilowatt out put will be a little less, but not enough for the small difference to become a problem. Expect about a 5% reduction in performance overall. If you burn Biodiesel at 100%, then you should turn up the fuel ratio about about 1/2 to 3/4 turn and adjust your engine timing by a 2* advance to compensate. You will still get through emissions with flying colors and you will feel it in your right foot.
2. Carry some spare fuel line hose with you in the trunk. Biodiesel doesn't like organic rubber and you will need to check your injector bleed hoses and change them more frequently.
4. Biodiesel gets a little cranky at colder temps and you going to have to mix with fossil fuel or kerosene to keep it moving depending on where you live.
5. It is not as easy to get as regular diesel, so you may want to store some at home. I have a 200 gallon fuel tank for this, but I live way out in the country. Use your own judgement. If your close to the source, a couple of 5 gallon jugs could work out just fine!

The Pro's outweigh the Con's for me and everyone I met feels the same way. I haven't really noticed the fuel economy difference everyone else seems to have, but your fuel economy could be a bit less. It is still worth it though.

Thanks to all for the helpful comments and information. I plan on trying my first tank full of bio this weekend to see how it goes.

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'81 240D 4-Speed 328K (Daily Driver)
'01 Cadillac SLS 135k (currently up for sale)

When I switched my truck to Biodiesel, I read somewhere about starting off with a lower blend and gradually increasing. I ran a couple tanks of B20, a tank of B50 and then a tank of close to B99. After a second tank of B99, I changed the filter and haven't had any problems. I've heard of people having filter issues when they go straight to B99, but maybe there filters were old when they switched.
I carry both filters in the car and would even if I only used petro.

There is some good info at this site. http://www.biodieselnow.com/
They have a forum as well.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Nope....it was definitely crap in the tank. Eventually had to replace the pickup scree and got 2/3 cup of black sand like crap out. The prefilter seemed to catch all of it, but it became a PITA to change it. Since I don't know the history of the car and with it's relatively low mileage when I got it, I would bet that it could have had previous fuel issues.
No problem at all since.

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100