Yes, I have it open all the time. I have it configured just the way I want it with all my science blogs and world news feeds. It's very useful. Don't use it for friends as much.
No. The problem now is that all the running events I attend (usually the trail runs) always post their pics to FB so if I want to go and see them, I have to reactivate my account. Otherwise I don't miss it in the slightest.
I uninstalled Facebook app on my smart phone about two years back to save on data usage and such. Now I barely go to my Facebook profile, maybe once a month or so to check if anything of interest popped