Jacon & I both got New Super Mario Bros. Wii for Christmas, so that will be the talk of the day for awhile on the blog. We both have dabbled a bit solo and played some multi-player. It's much easier and more productive to play by yourself, but it is still quite fun playing with others, just don't take it to seriously. ("That's what she said!") I would consider saving one of your save file blocks just for multi-player with your friends and family.
My biggest initial question was, what are the Special Gold Star Coins for?
Based on a little reasearch, you need to collect them all to open a secret 9th world when you finish the first 8 worlds, so if you are cruising through the game and not getting all the stars, at some point you will probably want to circle back and nab those coins!
As family, we also got the Wii Fit expansion pack, we have not opened it yet, but stay tuned for reports.