Here is my experience:
Tested it on outlook 2003, 2010, android phone (Samsung S4, S5 and Moto X) and an iphone 4.
During this initial testing things seemed to work well, I had to configure the outlook clients to poll the server every 3 minutes, had the sync errors due to lack of proper global address list support and I could not use Outlook Anywhere over SSL. These were all documented and not deal breakers.
After I went live with a small (6 seat) office all sorts of weird stuff started happening. My past experience is that 90% of "weird stuff happening" is caused by users doing things that I never expected them to do, but in this case the users were not causing the issues, it was all Zentyal/Openchange.
Quite often email would be accessible on the server through the Sogo webmail interface and on the phones, but would not show up on the outlook clients (especially outlook 2013), what was really odd was that one email would show up in outlook and the next 5 wouldn't and then the next few would. F9 and shiftF9 did not solve the problem, restarting outlook worked for outlook 2003 and outlook 2010, but not outlook 2013 (not that restarting outlook is really a "solution"). The users figured out that if they flagged the missing messages on their phones they would then sync to their outlook clients - I wrote a rule in Sogo to flag all messages, but that didn't work.
Next, on the outlook 2003 clients, the to and from email address fields would become blank on random messages (i.e. they would come in fine, with the to and from fields populated but during the next sync they would become blank and outlook would no longer display the message at all, you would have to go to the webmail client).
As you can guess random email delivery did not go over all that well with the users. We are now using a hosted exchange provider.
One other thing, I noticed that if I sync'd a calendar from outlook to openchange everything was fine; however, one time I had a problem with the outlook profile so I deleted it, recreated it and let it sync with Zentyal/Openchange/Sogo. After it sync'd the all day events now spanned two days. I checked the time zone settings on both sides and they seemed to be set properly. I tried to recreate the problem with just one entry (i.e. I created a similar entry in Sogo and let it sync to outlook) but this did not cause a problem... so then I deleted the entire profile, recreated it and let it sync with the server and sure enough all of the full day events now spanned two days.
Good luck to anyone trying to use this in a production environment.