Yeah, I agree with Grace.
It is something that you should really test out on your own market, but I charge a standard shipping fee on video games of 6.99. That price actually not only covers the shipping price, but it covers the item listing fee, final sale fee (in about 80% of cases), as well as PayPal fees.
In most cases it even leaves a dollar or two, which then goes to offset the monthly store fee. Of course the aim of this strategy is to have a cost neutral ebay store front to do business on, and I'm pretty confident that after our testing that we've got the formula worked out pretty well!
Now I do use free postage as a marketing strategy to compete with some sellers at times, and that also works, but I only ever use it on games whit a heavy margin to begin with!
That shipping price came about after about a solid month worth of testing, seeing what consumers would accept as a reasonable price. We average just over 4.7 at the moment on shipping price, and a big part of that average is speedy delivery.
As Grace said, if they get it quick they are less likely to mark you down. The games account is still only very new and not yet up to speed, but out of 202 feedbacks, we have had one neutral based on our shipping price.
Test your market, in fact I always suggest off-branding an account just for this purpose. Set up a second account, keep it identical to the original, then play around with some shipping options and prices, see which account is doing better business.
I would suggest testing the market for around 6 weeks, unless you are getting really solid data back over the first 4 weeks, then you can trim up the account to match your test results and that should have it pretty much optimised!