Haven't really kept up to date with the development of SC and only poked around their forum once or twice, but it would be great if someone would compile a list/comparison of features (planned and already implemented) for the two games.
All I know at the moment is pretty much what's planned for ED and that SC is going to offer walking around from the first release.
... oh yeah, and that the SC team has made a bit more money.
The number of differences is probably far too many to reel off. But despite their differences there will be a lot of similarities too.
Its probably easier to mention the 'theme' both games are aiming for.
Star Citizen is coming at this genre from an attention to detail aspect. Concentrating on micro details. Even the gameworld is scaled down to around 115 star systems since its gone the handcrafted route.
So SC will probably be stunning in the visuals and fidelity department but may be limited in its wider scope. No real science involved, planets will be scaled down - no celestial mechanics. No skybox, background will most likely be a paint job and not real points you can fly to. Cutscenes in place of freeform planetary landings, and landings are restricted to a few points of interest only. Combat seems paramount, exploration seems a secondary consideration. Ships seem be the be all and end all at the moment with stretch goal after stretch goal geared towards unlocking another type of ship that people can buy.
Squadron 42 will be SC's ace imho. It looks like its going to be a great mission run game with constant updates and mission packs.
Elite seems to have taken the opposite route. Concentrating on scale, scientific accuracy is important, ED will have a 1:1 scale galaxy with full scale worlds. FD seem to be pushing the full sandbox experience with players free to fly where they like and do what they like. Exploration seems paramount and combat secondary (in my opinion

). I don't see the same passion for ships from players in ED. People seem more interested in what you can do and experience in Elite rather than what you can fly (again personal observation).
Its also quite telling that CIG are encouraging SC players to mod the game and run their own servers. Either its a great selling point or CIG may see the persistant universe aspect of the game having only a finite lifespan before they hand it over to the community. Or it could prove too costly to keep upgrading - I read it costs $100K to add a new handcrafted system and even more to add a new ship!

As far as I know FD won't be allowing players to mod Elite or run private servers and have said all along they're here for the long run. Braben even said there won't be an Elite 5 since he plans to continue developing ED as long as players play it.