Missing church isn't sinful, but it can deprive you of good things.
Just like making a list of sinful/righteous things.
BTW,
why don't I ever see the question "is this righteous/clean?"
It seems like we're focusing on things either being "sinful" or "ok", as in "is it ok to watch the Simpsons."
And this mindset says a whole lot about christians - instead of living in the liberty and freedom and trust and righteousness we've been given, we approach life as if it was a mine field. But God hasn't set us in a mine field, but on a rock that will stand firm in the middle of a hostile world, even in the middle of our insecurity.
The rock is also referred to as Jesus. Church is fine, but I don't find my righteousness there. I find it in Jesus, who Himself IS my righteousness. I eat my breakfast, but it is God who sustains me. I try to do good, but it is God who justifies me. I try to secure myself from the world and from sin, but Jesus is the one who saves me.
That's why I can attend any service I like on whatever day I like, because He is my peace. That's why I'll leave the meeting if I get too tired, and it's the reason I praise God when I choose to stay in bed on a sunday morning while the early risers are in church.
I AM the church, therefore I can't miss it. I'm the church on sunday, monday, the sabbath, and every moment inbetween.