It is possible to install OS X on a RAID volume. I would recommend level 5 as a good mix of redundancy and performance. I think though that you may get better performance off of the internal SSD than the OWC RAID.
OS X client is quite respectable in a business setting. Any IT worker with any talent at all should be able to support it just fine.
OS X server is another story, and is quite a mess. It has been losing functionality since Snow Leopard. Open Directory is a complex, fragile, beast. I keep hoping that one of these iterations it will finally be solid and stable, as so many other services depend on it. About the only nice thing Apple has done recently to server...
We have an office of about 30 folks plus big groups of visitors for meetings. I have 2 Airport Extremes to cover wireless. They are one of the least problematic devices I've seen. I've not had a single problem out of them for years. In fact I kind of forget about them till an update comes out.
It seems like the change from Lion to Mountain Lion is much, much smaller than the change from Snow Leopard to Lion. I imagine that we'll see smaller changes with only a 12 month cycle, and hopefully updating won't be too big a deal. On the plus side with the faster release schedule we may see Apple keeping the open source components more up to date. Usually they would pick a version of OpenLDAP or OpenSSL and you'd be stuck with that for 18-20 months until the next...
Not really. In fact ML shows that installing apps from sources other than the Appstore will be supported for a long time. If they were planning on making the only source of apps the Appstore, they wouldn't have bothered developing Gatekeeper.
Perhaps you missed my post. Gatekeeper uses the current quarantine mechanic where downloaded apps are marked with an extended attribute of com.apple.quarantine. You can see this by using the -@ switch with the ls command. All you need to do to get around this is run sudo xattr -d com.apple.quarantine AppName. No need to change the gatekeeper level.
Gatekeeper is an extension of the quarantine process Apple already uses on downloaded apps. All apps that have already passed the quarantine prior to installing ML will pass Gatekeeper. Also, as a manual way around Gatekeeper you can just remove the com.apple.quarantine extended attribute and the app will launch.