But who can see it? That's what I don't have clear.
When I own a namecoin .bit domain, do I own it forever?
It's early days still. So people will need to adjust their settings to use nameservers with .bit support. Sometime in the future .bit may be added as an official TLD... but who knows
As for your other question, in the current system, you need to keep updating the name in the blockchain every some odd blocks (i think it works out to about a month?) but this is free.. so you own it forever unless you forget to update it once a month. But this is a fee-less update so you will never have to pay more than the namecoins you originally spent.