A C150 pilot failed to inspect the oil level and cap security prior to flight and discovered the cap open and much of the oil missing upon completion of his flight.

Narrative

I was climbing through approximately 1;200 FT MSL when I noticed a faint smell similar to heat. I checked all engine instrumentation and looked everywhere I could to see if there were any anomalies but found none. I got ATIS and contacted Approach but did not get a response due to frequency congestion. I circled outside of the Class C Airspace further attempting to contact Approach but to no avail. I then decided to fly west toward another airport so I would be in the corridor for another Approach frequency into my destination. Enroute I noticed a small misting of oil in the bottom right corner of the windscreen; again; I checked all available information in the aircraft to see if there were any engine abnormalities and could fine none. I finally got a response from the congested Approach Controller and got cleared into the airspace and to land on the right runway without any further difficulties. Upon taxiing back in and parking; I walked to the right hand side of the aircraft and saw the whole side of the aircraft covered in oil. I then realized that I had forgotten to check the oil before taking off and that; apparently; the pilots flying the aircraft prior to me either did not secure the dipstick sufficiently or intentionally left it open prior to my flight.