This comparison is purely speculative, no investment advice, and, assumes all 21 million Bitcoins are produced/circulating. Since there aren't that many BTC on the market yet and most probably some have been lost in wallets I see this as highly approximative and conservative but still interesting.
The current market cap of Bitcoin as of writing is $32.6 billion which equals to a value of ~ $1,550 / BTC if all coins were generated. In the table below you can also see that it has a similar valuation to Silver as BTC is a little more than double.
If you compare potential market capitalizations of BTC to the real world it gives you interesting numbers to tinker with.
In my opinion BTC still has a long way to go in order to reach high valuations like Apple for ex., and is ages away from Gold but it has already overtaken Silver and the speed at which it spreads is growing at a fast rate.
Sources: