I was a relatively heavy Hackpad user (still using it, actually) and have been beta testing Notes/Paper for a while - it started off very Hackpadish, but has evolved a bit, enough that it may actually be suitable for my small company to finally migrate off of Google Sites.
For me, the biggest missing piece for Hackpad, and why it was always a non-starter for any serious knowledge collection purposes was its lack of hierarchical structure. A few weeks ago, Paper finally added support for folders, which while still a bit clunky/not-ideal (the sidebar doesn't give you a tree nav, there's no way to see the whole structure), it at least meets that minimum bar for organizing say, more than 20 notes.
I haven't done much group collaboration work (the teams/org stuff was just introduced, and honestly, the thought of Dropbox completely messing up my/my coworkers personal Dropbox accounts terrifies me - the horror stories posted in the thread don't help assuage my fears, and I am not sure I have a conceptual understanding/trust of how Dropbox models accounts/teams), and while Folders have permissions, I can't figure out how to assign/inherit permissions (crucial for working with clients, contractors), but on the bright side, it's not literally insane like Google Sites' permission system (it involves modifying global inheritances to give access to specific sub-trees).
In most other ways, it is like Hackpad++ - mostly like you would have expected it to evolve: great feeling typeahead search, instant editing, OT-based multi-user editing, and improved/extended embeds, and adds annotations, which I can see being conceptually pretty useful.
The biggest thing missing for me now is offline editing - it's not strictly a requirement for our office use, since that's online-only as well, but there are so many times traveling/offsite where it's a huge pain. The other things are mostly niggles - ways to actually see the site/document structure, the option to attach files (especially images) w/o them being directly embedded, a way to view/track embeds/media/files only, but overall it may be the best wiki-like app out there for small groups now, especially those that hate traditional (modal editing) wikis.
Dropbox two account works great. It's specifically designed to keep your personal Dropbox completely separate (and unscrewup-able) from your company assets. We built it because people had been intermingling personal Dropboxes with company assets and it created messes for them when they left the company, etc.
Anecdotally, I've had my personal Dropbox account since 2007 (was one of the first 1000 beta users), and my family manages tons of stuff in it. I started using two account in 2013 when joined Dropbox (the company), before we released it publicly. Your existing Dropbox gets moved to "Dropbox (Personal)" and a second folder gets created called "Dropbox (Your Company)". Nothing changes about the behavior of "Dropbox (Personal)".
No problems whatsoever with the separation of personal and company--and that reflects the vast majority of our users' experiences as well onboarding a team.
As another user in this thread mentioned, Dropbox doesn't support 3+ accounts, so if you work for multiple companies (who all use Dropbox), that might be a problem.
Just a guess, I think the other problem report in this thread was someone who wasn't expecting Dropbox "for teams" to create a completely new type of account for everyone at his/her company. They probably use basic or pro accounts in an ad-hoc way at their company and were unfamiliar with the teams product and the fact it is distinct.
