How much omisego do we get for 1 ETH?
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.
Exactly, you get an "airdrop" valued 0.1% of what you already have in Eth. This means that even the act of checking your Eth wallet to see if you've got some OMG is not worth the effort... unless you are an Eth Whale. But then, again, you are already rich and so still it is not worth the effort.