Facebook probably doesn't deserve the label "monopoly" - but still I think it's a major problem that "everyone" expects "everyone else" to have a Facebook account.  I still haven't joined Facebook, but it's sometimes making things difficult for me, and I know people that have missed invitations to weddings and similar due to not being at Facebook.

As I've written in my post, Microsoft is losing some of the grip on the markets, but it's still pretty hard i.e. to buy a regular laptop without paying a "Microsoft tax" - and I'm regularly getting into problems both from my children, my wife, the childrens school and other instances for not providing Microsoft Windows and Microsoft Office at home.  Microsoft still has a pretty good grip on those things - you may argue that they don't qualify as a "monopolist company" due to the mere fact that alternatives indeed does exist, but the problem doesn't go away by arguing over definitions.