The overly simplified way of looking at it: Apple as a company is now worth more than Walmart, the world's largest retailer. Granted, market cap is only one way of gauging a company's financial worth, but considering the pile of cash Apple is sitting on right now, it doesn't seem like a huge stretch to say that Apple's economic worth is at least very closely represented by its position in the market cap rankings.
Some firms are predicting that Apple will eventually catch up to or surpass Microsoft's market cap. While there's currently a $41.77 billion dollar difference between the two companies' market caps, that's not a completely insurmountable gap. Get a load of this batch of perspective: ten years ago, Microsoft was worth in excess of $586 billion, while Apple was worth a relatively paltry $17 billion. In the same amount of time it took for Microsoft to lose almost $330 billion in worth, Apple's market cap rose by nearly $200 billion. No wonder Fortune named Steve Jobs "CEO of the Decade."