I haven't experienced any problems with this... It looks like a lava lamp in the syringe, but as long as you inject slowly (let your muscles tell you how fast they can take it), then I've never encountered a problem. The analogy above about pushing hard to get the oil out and then rocketing 1cc+ of water based gear into your muscle is a sure recipe for a sore injection site at the very least and possibly abcess on the extreme end.
Abcess...? I'd like to know how someone is getting an abcess from a reasonable dosage (for the injection site being used) injected at a reasonable rate.
Infection...? If you're practicing sterile procedures for drawing and injecting, there's nothing in an oil + water based injection that can cause infection.