A word of caution. Based on the good news from the last couple of posts, I checked my missing groups, and sure enough, they were there, but one that has about 100 members was only showing 3, and another with 21 was only showing a few.
A previous experience of this nasty phenomenon last year went through a similar stage, but after a further period of time, the whole group came back.
Meanwhile, still no sign of the changeover to the new version of Outlook.com which is supposedly being rolled out, US of A first, and the rest of us later on. Perhaps if you are a resident of USA, you might comment whether this has come to pass for you,
and if so, whether it is the best thing since sliced bread, or all hype and no substance. Particularly, whether the new "lists" feature carries over your previous groups, and what happens to those groups/lists when you look at them in People in Office Outlook.
(As I've said previously, they are available as "categories" in list view)