You are going to love it. Make sure and follow the instructions on starting, and especially restarting when hot, that are in the owners manual. These auto tune saws are not the same as older models in that respect and cause some people grief. My 550XP makes me smile everytime I use it.
I put a sweet muffler on mine I got last week and haven't had a chance to use it yet since I had to leave for work. It sure sounds mean and should give it even most ump. Stock muffler in first picture vs modified one
Nylimited - I'd suggest waiting until your warranty runs out to replace the muffler or do any other mods. If you just can't wait that long, at least give it several months of good hard use first. If there is going to be a problem, it usually shows up early on. No point in causing yourself hassles if you have to make a warranty claim (and at least save your old muffler to put back on if you have to bring it in).
Had a chance to run two tanks of fuel thru it yesterday at first I thought it was a little doggie then it woke up and wow. So far I really like this saw runs fast and smooth.