Not a huge amount.
If airdrop is 5%, then using approximate figures... OMG cap is $800m, so 5% is $40m. ETH cap is $30b. So ETH cap is about 1000x OMG total airdrop value. So for every $1000 of ETH you hold, you'd get $1 of OMG.
It's nice, but not worth getting excited about.