Looks like a neat idea, here are some ways to do it better:
-Clean the mill scale off the portion of your tubing where you're going to be welding. Inside and out. Scotchbrite pads, emery cloth, whatever. Just get that stuff off of there. It will make the welding much easier/cleaner and also make the joints stronger.
-Ditch the gusset. Unless you are doing *serious* FEA work and can model what will happen, you are more likely to create a nasty stress riser than improve the longevity of the frame. The gusset you have added there is pretty much a textbook case of what not to do (good discussion here: Gusset length & butted tubes)
-It looks like you're getting some pretty gnarly oxygen contamination of your welds. You shouldn't be seeing a lot of grey/black, you should see shiny uncontaminated metal. Consider getting a gas lens and doing some experimenting with how much Ar you are pushing. Travel speed and/or torch angle could also be issues. I would personally not let something with welds that looked like that end up in the hands of customers, but that's up to you.
We are taking deposits for the new 2014 Design Logic "Da-Phat" this bike will have the same spex as our "Da-Trail" but have a 170 rear dropout spacing and be able to fit surly 100mm clown shoe rims and Bud and Larry 4.8 tires. the rear triangle and wheel will be built symmetrical and able to be swapped out for a 29er for riding enjoyment year round. Frames will be $1495 with choice of powder coat paint and be shipping late spring, early summer.