Hi Cristian,
I made a quick search using keywords "image stabilizer birds in flight", Google search engine returning 100k + hits. I restricted the search to pages freshly updated (updated during past year)
There seems to be a split opinion on this topic.
Do we know that the IS is impacting the AF performance on Olympus bodies? Is there a source that confirms this? (This would be a valid point).
Samples of arguments for/against:
Speaking in favor of IS off:
http://www.evergladesphotosociety.org/articles/flightpart01.html
Turn the Image Stabilizer (IS) or Vibration Reduction (VR) of the lens off. Most people think that the best setting is to leave the image stabilizer on and to set it to panning mode. However the image stabilizer slows down the auto focus system, and faster auto focus is more important than image stabilization, especially at shutter speeds of 1/500s and faster.
http://www.brighthub.com/multimedia/photography/articles/75369.aspx
This is a feature which is of use when using slow shutter speeds and low light. As we’ll be using fairly high shutter speeds of 1/500 and above, the only purpose image stabilization would serve would be to reduce auto-focus speed. I would recommend to switch off this feature.
Speaking in favor of IS on:
http://improvephotography.com/743/tips-birds-in-flight-photography-animal-bird-digital/
Bird Photography Tip #10: Don’t skimp on Image Stabilization. It is unfortunate that image stabilized lenses often come at a premium, because some photographers opt for the cheaper lens without image stabilization. Especially for telephoto lenses, your image stabilization will be absolutely vital to the success of your photography of birds in flight.
http://jefflynchdev.wordpress.com/2011/01/10/getting-tack-sharp-wildlife-shots/
Birds in Flight
Shutter Priority (Tv)
Shutter Speed 1/500th or faster
Center AF Point
Evaluative or Spot Metering
ISO 100 – ISO 400 to obtain a 1/500th minimum shutter speed
AI Servo Mode using Back Button Focus (allows me to switch between One Shot and AI Servo)
High Speed Burst
Image Stabilization turned ON – Mode 2 (Panning)