Top dome doesn't quite line up perfectly with bottom dome. Should I be concerned?

I would wait for the warm weather and search this forum and YouTube and follow the instructions. I had the issue as well and spent about 1/2 hour getting it in line.  Overlap on one side is under lap on the other and will expose the gasket to direct heat.  Worth the time to fix it in my opinion.  

Yes, your egg is defective.  Please ship to me and I will relieve you of the burden

I have this issue as well. Where the hinge mechanism and springs are located on the back of the egg is short about 1/3 of an inch. The front has an underbite(the dome needs to come forward about 1/3") and after loosing the bands and hinges i got nowhere. Going to try with a 2nd person soon. Local dealer said to measure both dome and base to compare, sometimes they come out warped or not lining up and they would replace free if covered by guarantee.

Based on the video above, adding spacers fixes it? That was 1 of my initial thoughts. Anybody else done this with success?

Theres a bigger gap after this last cook 

If you don't have smoke leaking out when you cook than I wouldn't worry about it.  Enjoy the new toy!

@RRP shared this with me when I had an underbite issue. It solved the problem

"I called this morning and spoke to Dewayne at BGE HQ Customer Service.  He was extremely helpful and guided me through the steps to level out the top.  It was extremely simple to do, even for someone who didn't understand the way these things are put together. 
So basically here's what was the problem and what I did.  The first problem was that the lower band was not wrapped around evenly - it was lower in the rear than in the front.  He explained to me that the lower band should come right up to the edge of the lower gasket all the way around the lower half.  So I loosened the carriage bolt on the lower rear band and GENTLY tapped along the band using a block of wood and a rubber mallet until the band was placed evenly around the whole bottom.  Then I tightened the band.  From that point, the underbite had improved significantly, but there was still a bit of unevenness along the planes where the gaskets met and it still did not pass the dollar bill test.  In fact, the gap on the rear side between the gaskets was slightly worse, but I wasn't worried because I knew there were a couple more steps to 
Next step was to adjust the front to back placement to fine tune the sitting of the top to the bottom.  There are two slotted acorn nuts on the top part of the hinge (above the spring) on both sides of the top that needed to be loosened so that I can 'wiggle' the top into a centered position.  So I loosened all 4 nuts, wiggled it into position, then tightened.  Now the top was centered properly (no under or overbite), but there was still unevenness on the plane of contact - in other words, it still failed the dollar bill test. 
The last step was to somewhat repeat the first step (loosening the carriage bolt) except for the upper band.  Wherever there was the largest gap between the two gaskets, I GENTLY tapped the band upward which essentially pushed the lid downward by it's own weight.  Once I saw that the upper band was positioned in such a way that the entire top part of the egg sat nicely and evenly on the bottom, I tightened the carriage bolt of the top band and vuala!  It was fixed.  Dollar bill test passed all the way around the egg.  No more underbite (or overbite). "

Golfguy77 said:

If you don't have smoke leaking out when you cook than I wouldn't worry about it.  Enjoy the new toy!

this!

welcome!

My small was a little out of alignment on the sides. Added a washer and now its fine.

I removed the dome completely off with the band attached and then reattached after raising the bottom band evenly across the very top lip of the base and then connected it together. It worked for a bit then the dome slipped back into place and it still has an under bite. It actually tore off part of my gasket...how hard to i tighten the band? Last time i was slightly loose and slid, but i dont want to crack the dome or base either from too much pressure by over tightening the screw.

@bgeaddikt ... here's a pretty good article about band replacement/tightening:

http://www.grill-repair.com/blog/2013/big-green-egg-spring-assisted-band-replacement-instructions/

This is the paragraph in the above article that answers your question:

Do Not Be Alarmed when the bolts bend from the tension.  This Is Normal.  Just like we learned in high school history (Roman Architecture) the ceramic dome is incredibly strong and will not break because the curve of the egg is truly a circle and the tension from outside the circle forced weight to distribute around the circle to strengthen the egg structure just like the old churches and bridges with arches that supported so much more weight than the strength of the brick should have been capable of supporting.