I think it depends on the register. If I'm talking at a business meeting I'll likely be much more aware of my grammar, whereas if I'm down the pub chatting with friends I'm not going to concentrate or care about my 'correctness' to the same degree.
'Was' just sounds wrong. Perhaps it's just me, but it doesn't seem right. Keep in mind I have no evidence to support this, but it just doesn't sound natural.
Actually, and I just came across this myself about a year or two ago, both are English: past and present usage; They express different meanings, though:
The subjuntive use of the verb were in If I were expresses a condition that does not exist, one that's contrary to fact, whereas the indicative use of the verb was in If I was expresses a condition that 'was' probable, likely or could possibly be true.
1. If I were you (which I am not) I would take the money and run.
2. If I was you (which I most likely might be in that situation) I'd take the money and run.
The poll asks us to make a choice between subjunctive and indicative moods:
If I were is the subjunctive mood. If I was is the indicative mood.