Well the wife and I played the hell out of it Sunday... and Monday... and Tuesday... and a little bit yesterday.
It's loads of fun. As others have said, the game only forces you to calibrate when you first start it up, or if you perhaps leave it running for 5+ minutes and the wiimote shuts off, then you come back, the first game you play asks you to lie it facedown.
Tiger Woods I don't ever doing any calibration in-game. I know the game manual said something about placing the Wiimote facedown to re-calibrate if you felt it was out of whack. But you didn't have to pause or anything. I think I might have done that if I ever had to take a break and came back and the wiimote had shut down.
Anyway both my wife and I have gotten really into the Swordplay. And while running the showdown mode we have both started pausing and setting the wiimote down before each round. Seems like the swinging can really knock it out of whack. Maybe we're just being overcautious or something.
But I've played through an entire 18 holes of golf and disc golf and never felt like it was out of whack. So I guess it just depends on the mode and whatever.
True test of the game will probably be when I have my parents over to play. They're on vacation right now, so in a couple weeks I guess. But they absolutely love bowling and tennis from the first game. Curious to see if they will adjust to ping pong in this one and if they will find any of the others interesting. I'd think they'd enjoy 3-point shootout as our whole family has always played a lot of basketball, but we'll see.
I'm more than satisfied with the purchase for myself though. Of course after first playing Tiger Woods 10 over a month ago, I was sold on M+.
Oh and if anyone is wondering, TW10 beats the hell out of WSR golf. For serious players or casual players either one, TW10 is superior. WSR keeps the same ridiculous "swing too hard and you randomly hook/slice" BS that Wii Sports had already.

Dumbest design ever, still. And the putting... well it's just shitty compared to TW10. The putting in TW10 is just so amazing, if you play enough you can stop looking at the power meter even. But WSR golf never has that precision feel to it.
As for disc golf, it's a much closer match. WSR disc golf might be a bit more challenging. It's hard to tell how much of it is the limited aiming and difficulty telling how far away from hazards you are vs. how precise the actual throwing motion is measured. TW10 has the "can't miss" putter disc, but WSR is much easier to hole out on a par 3. They're both fun in their own way.