ISK (the in-game Eve Currency) can be exchanged for PLEX (the pilot's license) which can be swapped real world money, meaning players can buy in-game items with real world money - but not vice versa. Many players earn enough from playing Eve that they can pay for their subscriptions in ISK.
Similarly, the market is so complex and so real, that CCP has an in-house economics team, headed by the amazingly named Dr Eyjo (pronounced 'Ao'), who track every shot that's fired and every rock mined. They run a laissez-faire economy, which means that if someone untrustworthy screws up your corporation and destroys everything you've worked for, for months or even years, and you ask CCP for help? Tough. Giving untrustworthy people access to all your cool stuff was your mistake, not CCP's.
Similarly, there are some boring-sounding elements to Eve that further deepen that immersion into the universe; players need both insurance and clones. Insurance pays for a new ship when your old one gets turned back into moondust; clones pay for a new you if you get killed (which you need, as death really screws with all the skills you've spent years learning.) And the ships themselves are amazing varied and complex, with all sorts of customisable modules, ranging from cheap fighters a few meters long, to exotic T3 cruisers a few kilometres long built with material gathered from the dangerous space beyond wormholes.
These boring bits are the foundations for the most compelling part of Eve - which isn't the combat, no. Nor the player pirates camping at jumpgates. It's the politics. And it's terrifying.
There have been cross-system wars in Eve that have carried on for ages - for example, the Great Northern War lasted six months in 2004. Indeed the wars between the B.O.B. (Band of Brothers, a huge alliance containing a peak of 3,100 pilots) and Goonswarm (the Something Awful forumites, allied with a bunch of other corporations) went on for years, until the B.O.B. had their alliance director betray them, steal the corporation's assets and dissolve it. The Mittani, the head of Goonswarm, is in many ways more powerful than the developers of the game.
The three languages available - English, German and Russian - make the game's single-shard game universe (there are no server variants like other MMOs) complex enough, but soon the Japanese will join in. As Eve is hosted on a single supercomputer in London - called Tranquility - soon there will be 500,000 players welcoming a new Japanese contingent to their battles.
Finally, it doesn't stop there. The cross-platform integration with the upcoming Playstation shooter Dust 514 (means that Eve corporations will be able to intervene in PS3 FPS battles - firing from orbit on their enemies or employing mercenary Dust 514 corporations to capture planets for them. It's been implied that the Dust players will also be able to shoot back into space - and, possible, even travel to the stations that orbit these planets to meet their Eve brethren face to face.
Eve is basically a supercomputer that hosts the most realistic game universe ever seen, that will soon integrate with PS3 and that has half-a-million people from all over earth battling and plotting at any one time. If you've got six months to spare and want to try the cutting edge of gaming, dive in. Don't say I didn't warn you though!