I have this really firm rule about filtering - I'll only do it if I can see that traffic is gridlocked for at least 2 blocks. I know that one thing that really annoys motorists is when cyclists filter to the front of the lights when they are red, and then they have to go around the cyclist 100 metres down the road. In this instance, it's 5pm - peak hour - and traffic in most locations around the city is at a standstill. The place is a parking lot from end to end. At times like these, I have no problems using the bike to get ahead.
The thing is, it still pisses off the occasional motorist. In these circumstances, me getting ahead has no impact on their progress. When I am half a mile down the road and turning right, they'll still be sitting in the same spot. They're just annoyed at the idea of anyone getting in front of them. I imagine people like that get irrationally annoyed at lots of things. So long as they don't open their car door on me as I go past, I really don't care.