It's dynamic, but only in relation to the menu which is maximised. All of the other options are there, you just need to click on them.
Compared to 'dynamic' menus in the old version (i.e. everything greyed out), it's much better. Plus it's right 80% of the time, which means greater productivity 80% of the time at the cost of an extra click 20% of the time.
First of all, I'll concede that 80% figure. If it were any lower no one would ever use the damn thing.
But, it's not "an extra click" the other 20% of the time. In my experience, and that of my cow-orkers, it's more like "roll the cursor over every icon in the current ribbon thet you don't immediately recognize and read the Tool Tip, in case the command you want is cleverly hidden in plain sight, and if you don't find it there, click through ALL the tabs at random and repeat the Tool Tip thing until you stumble upon the command wherever Microsoft decided to hide it, and when that doesn't provide joy, open Help and click on a half dozen different topics until you find the treasure." That's the part that gets really, really old, really, really fast.
Listen, on a certain level, I give Microsoft a lot of credit for trying to simplify their UI, and take it to another level. But as it always is with MS products, the problem is in the implementation. It is NO exageration to say that 90%+ of the people I now and work with who've had the misfortune to be forced to use Office 2007, hate it with a white-hot passion generally reserved for child molesters or GWB. If it works for you, then vaya con dios, muchacho. You're one of the blessed.