So, this is based on the current sharepoint installation at a Fortune 25 company.
Automatic notifications of changes are great. Workflows might be ok, but I've seen very few sites using them internally.
There is no collaborating on a document at the same time. There's a checkin/checkout model. While Excel offers true simultaneous editing of a file on a shared drive, that's gone if it goes in a sharepoint. Documents with OLE linking don't work. It has some limited BI capabilities, which is nice, but it's hard to embed real BI solutions (BizObj, Tableau, etc) into sharepoint so there are either links or we're dropping exported files in a document library. It would be nice to send links to people outside our company (and you can define federated identity) but that definitely requires a lot of configuration to make happen. (It's not currently set up in our company.)
As it is, since everything in Sharepoint seems to site-based, we have hundreds of individual sites across multiple sharepoint farms. There's no global way to search all share points. When there is a search, it's really, really bad compared to what people get from Google. (And glacially slow compared to google, but I suppose if we dedicated google-scale infrastructure to sharepoint, it might be better.) As a result, people do not use search. It's almost never a successful tactic. There's no automatic clustering of content like "See Also" or "Related documents".
Most groups end up using a single document library as a shared drive and maybe add a shared calendar. Meeting sites are set up by very few groups only for standing meetings, because it's a lot of work for each meeting. If one is set up, that information is siloed away from everything else. The wiki pages work, even though they aren't as easy to use as a normal wiki.
I'm sure that all of these problems could be fixed by working hard enough. That's my point: Sharepoint is a tool that groups could use to build a decent information sharing platform, with suitable care, planning, adoption of third party apps, etc. It's not a good information sharing or knowledge management tool out of the box.
And yes, there's a reason that it's used by tens of millions: it integrates with the Office products and is sold alongside the other MS enterprise offerings, and is therefore bought by lots of IT departments where the purchasers of the software are separate from the people who end up having to use it.