Maybe "new" is too strong of a word, but it's never been played in a master vs master game, according to 365chess.com.

I played it today and won with it, I must admit it wasn't a brilliant game, but was good enough. Houdini evaluates the position as +0.15. 

Although it has been played in a few non-master games, apparently.

What move did you play next? It still looks really unclear to a newb like me. I have no idea where I would go from here.

6 Bf4 is a lot better I think

If you have Houdini, what the heck do you need us for???

Thats just a slav defence except with an ugly 4... a6

I know that it's the Slav Defence... I even put that in the annotations... -.-

New opening- variation, you know what I mean.

Actually, it is fairly common at master level.

http://www.chess.com/opening/eco/D15_Slav_Defense_Chameleon_Variation

5 Bg5 is rare because it's premature - Black should just continue with 5 ...dxc4.  If White wants to play Bg5, he should wait until Black plays ...e6, so 5 a4 or 5 Qb3 first, and if Black replies to either with 5 ...e6 then White is on sounder ground with Bg5 because of the pin.

5 ...Ne4 isn't good, and 6 Bf4 or even 6 cxd5 is preferable to 6 Nxe4, which only helps Black solve his opening problems.

I'm not familiar with Houdini, but engine evaluations are given in units of pawns, +1.00 being a solid pawn ahead.  +0.15 is roughly 1/6 of a pawn, or half a tempo - about what White starts the game with, so that's not a favorable result for a variation.

I would suggest that Houdini's assessment may alter after a few moves are made (and black catches up in development).

Even though black has the pawn, the computer sees White's development as compensation. I think White's lead in development will be temporary and that there isn't much to be gained from it in the current position - so I think the pawn will start to tell in the next 10-20 moves.

Would be interest in what line Houdini gives. Have you played the moves down the line so that Houdini can re-assess after each move (rather than assess at the end of one long variation)?

Reb vs DafddTheIgnorant with a6 Slav!

Ultimate shame sounds good to me.

Either that or to work...