When the world saves you will freeze for a split second up to 2 or 3 seconds depending on your rig. This happens to everyone. Next time you notice it check out the the top left or right corner of your screen (I forget where it is) and see if it says world save.

If that's not it I'm not sure what to tell you. The game isn't optimized yet and there are some really bad desync issues in multi player, as well as serious performance hits when you do a lot of land Terra forming.

I played for about 18 hours with the game running very smooth. No crashes, or stutters (other than the normal periodic saving stutter). I logged in the next day, have done nothing to change my computer, did not change any game settings and was getting stuttering before I even made any changes to the game from the night before. Now the game has a 1-2 second freeze every 18-25 seconds or so. It does not come in spurts and does not seem to be affected by having ten mobs around me, or by anything I am doing. This ranges from annoying when I am just running around to a real hindrance when I am say fighting a troll. This seems to have been an issue for awhile and though I was enjoying the game, it may turn me off from playing much further if it is not dealt with.

Mines stutters too, and has been since Hearth and Home started. Didn't have that problem, other than the world save, before that.