While my overall testing of 10.11 El Capitan has been quite favorable (in stark contrast to my run-ins with Yosemite; knock on wood), I've found that getting the thing to install properly in the first place is a bit of a challenge. I haven't found much satisfaction in the way of solutions elsewhere online, so since I think I've found my way out of it I figured I would document it here in the event it can help somebody else. This is all, in a word, ridiculous. However, "it just works." Fortunately for me, I have over a decade of experience struggling with Windows to prepare me for such problems, but still... I expect more from Apple and I see this as yet another instance of a product lineup (if not an entire company) slowly going to seed and nudging me towards a jump to Linux. Background: About a week ago I decided I would trial 10.11.0 on a separate partition on my 2012 cMBP, clean install. I have 10.9.5 installed on a 120 GB OWC SSD drive out of which I carved a separate partition to try 10.11.0. Also on-board is my OEM 500GB HDD which I was able to keep thanks to OWC's Data Doubler package. The Process: I created the bootable installation flash drive through Terminal as documented in several places; option key on reboot; that whole thing. The installer is slow to load (much slower than 10.9 anyway) but it eventually does and I select the drive and get going. The progress bar starts out "17 minutes remaining..." and runs until it's finished - or so it says. It hangs at "0 seconds remaining" and an inspection of the error log reveals a near constant loop of the same "Language Chooser...TSplicedFont failed creating descriptor for:" error as described in a thread on Apple's Support website here: https://discussions.apple.com/thread/7263067. This will continue for a couple tens of thousands of lines of error logging before a dialog finally pops up saying the installation failed, try re-running the installation; blah blah blah. As would eventually become obvious later, nothing at all was done for those 17 minutes and the SSD partition was still empty. But wait, there's more! I wouldn't find out that there was nothing installed immediately, because upon reboot with the installer and running Disk Utility, I would find that my SSD was completely gone! So after brief moment of, well not really panic but more disbelief, I found that flashing the PRAM might fix this and sure enough it did. 10.9.5 booted up and things were the same as normal. It was then that I found a pristine 10.11 partition. Subsequent testing would reveal that no combination of SMC resets, PRAM flashes or creating the install media in Disk Maker X seems to solve this problem. Nor does attempting to install on a completely wiped Mac (SSD and HDD) make any difference. (Yes, I made backups before all this; in duplicate in fact.) My Solution: What I found was that the installer would run perfectly fine if executed from within a working 10.9.5 session. Simple as that. With the Mac wiped completely, I installed 10.9.5 to the HDD this time and used that to execute the install of 10.11 to the SSD (I suppose I could have installed 10.9.5 to the SSD again and just wiped that partition afterwards but my obsessive compulsive will not allow that ). After the successful completion, I then re-wiped the HDD. Being an ex-Windows user, that's still not as "clean" as I would like it but it'll have to do. Now, my other Mac is a mid-2011 MacMini in which I also installed an OWC Data Doubler package and a 2 TB HDD. I don't really have the luxury of wiping the HDD there so I was trying to figure out how to manage that upgrade once I get to it. Turns out, I still have its 500 GB OEM HDD in a closet so I'm going to purchase an external case for it, make it an external boot drive and use that to boot the Mini onto which I can then clean install 10.11 onto the SSD. Ditto if I decide to clean install my wife's 2014 MBA (which has no luxury of a 2nd drive at all). I don't currently have a portable external drive, so there may be some other benefits to the arrangement as well. Hope that helps!