I got to play at the Born of the Gods prerelease and managed to get 2nd place.  Not bad as I got a few packs of the new set.  To be honest though, not much in the new set excites me.  Regardless, I picked up some stuff from the prerelease that I felt would be good additions to the cube.

Red
I took the dragon as my pre-release promo because the art looks cool and the ability is quite relevant.  Charmbreaker Devils was kind of a niche card and although it helped the Izzet blitz decks, it cost too much.  Izzet blitz wants to win quick and a 6 mana creature just doesn't do that.  The dragon also makes Utvara Hellkite and Scourge of Valkas more useful.

I decided to remove Foundry Street Denizen because I removed a lot of the cards that made the goblin more effective (Goblin Rally and Krenko's Command).  Impetuous Sunchaser is still aggressive and with the right auras can be quite scary.

White
Phalanx Leader was hard to use outside of a dedicated mono-white weenie deck and I felt that Akroan Skyguard would make for a more consistent GW heroic deck.
Loyal Pegasus added more consistent aggressive evasion as it only requires 1 other creature instead of 2 other creatures.  It does kind of become useless though if it's the only creature you have but in an aggressive weenie deck, that probably won't be likely.
I liked Ornitharch at the pre-release.  Either it's a 5/5 flyer or a 3/3 flyer and 2 1/1 flyers.  Both forms are good in my opinion.

Green
Courser of Kruphix is an interesting card and I don't have anything like it in my cube.  I still don't fully understand its uses but from what I've read it makes green decks better.  At the end of the day it's a fairly efficient creature and will help with mid-range decks.
I like tokens and Fated Intervention is one heck of a token generator.  Instant speed for surprise blockers or if played on your turn can help smooth out your draws.
Raised by Wolves provides more tokens and another useful aura.  Should make heroic decks easier to build with more auras.  Also it goes well with Howl of the Night Pack.
Karametra's Favor pretty much does everything Gatecreeper Vine does and then some.  The aura ramps and is a decent heroic trigger.  Does dilute the defender theme a bit so makes Overgrown Battlement and Axebane Guardian slightly worse but I think the trade-off is fine.

Black
Herald of Torment makes early black aggression even better.  Plus it has awesome late-game potential compared to Arrogant Bloodlord.

Blue
Despite me not liking to play against counter spells, I felt my cube needed a little more.  I originally wanted Nullify but I did not get one in any of my packs.  Thassa's Rebuff does encourage playing permanents though which is what I want.
Although Sudden Storm isn't strictly better than Frost Breath, I felt the scry addition is powerful enough to make the swap.

Other
Chromanticore is such a fun looking card I couldn't resist.  No idea if anyone will ever try to make a 5 colour deck but this could fit in so perfectly.  Gonna miss Ulamog's Crusher as it is a good creature and fits any deck but it will be fun to see if anyone will make Chromanticore work.
I was never fully happy with Korozda Gorgon as it's ability depended a lot on whether you could get enough scavenge or green evolve creatures.  With Graverobber Spider you can at least use its ability without depending on anything else other than creatures dying (and creatures will die).

I managed to pick up 2 of the 3 temples for this set at the pre-release but I haven't included them in just yet.  I'm probably going to wait until I have all 10 temples (currently I have 7 of 8) before trying to figure out how to include them.  I currently have all the Keyrunes and Cluestones slated to be replaced by the temples but I'm not sure about that.  I really want a way to fit the Keyrunes/cluestones and the temples so I can have lots of colour fixing and some acceleration.

There are a few other cards from Born of the Gods that I would like to add to my cube but I will have to wait until the set is fully released before I can pick them up.