Before the beta police start replying to my posting, YES, I know I am running beta software and I know there could be and will be issues. I have El Capitan installed on an external WD Passport HD, a second 512 GB SSD in my Macbook Pro and a second 1.5 TB partition on my iMac's 3T Fusion Drive. It is not installed on my well working Yosemite 10.10.5 HDs, the ones I use as my working HDs. Dear Tim Cook and/or anyone at Apple who cares about your customers, I have beta tested Mavericks, Yosemite and now El Capitan. I can say that my experience with El Capitan has not been fun and I continue to have major issues even in public beta 5. I should have predicted my problems with the beta 1 install which caused a kernel panic on my MacBook Pro upon restarting. I have lost count of the number of times I have had to reformat, download and reinstall an El Capitan beta after it was thoroughly trashed because of crashes. El Capitan seems slow, very slow at times with the frequent appearance of the dreaded spinning but redesigned beach ball. Just yesterday, I was typing a simple document in Pages and every 30 seconds or so, the beach ball spun. I get these periodic slowdowns where web pages won't load, programs launch slowly, the Finder takes forever to populate a screen and the beachball just seems to show up at random times. I've tried restarting the programs but the slowness remains until I restart El Capitan. Then El Capitan with the same exact configuration takes twice as long to boot up compared to Yosemite 10.10.5 even from a SSD. Launching your App Store program is exhausting. That little spinning thingie just spins and spins and spins sometimes never displaying a menu. And then there is Mail. The El Capitan's Mail program has finally convinced me to switch to Postbox. Mail v9 simply would not consistently connect to any of my Yahoo accounts. It was not Yahoo's fault since other PC's and other OS's connected fine. The current version of Mail is dreadful and Tim Cook, you should be ashamed of the people hired to write it. It is mind boggling that a v9 program would have so many bugs, be so slow and have constant connectivity problems. And it still has less features than its predecessors. Once Mail crashed and took out El Capitan with it. I tried restarting my machine and it would not boot. I switched to Postbox and the speed is incredible. It has never failed to connect to any of my 6 email accounts. It just works. Good bye Mail forever. And please don't get me started on SIP. I can see the need for more OS security but all or nothing is an incredibly poor choice. I am lost without TotalFinder, a program that makes Finder 10.11 what it should have been 5 OS X versions ago. I just opened the About Finder to check the Finder version number and I got the spinning beachball for 5 seconds. Grr! Apple should have a method for legitimate developers to get access to the underlying code in El Capitan. It is ridiculous to shut out developers who have spent a great many hours making my Mac experience better. Tim Cook: You should be ashamed of your El Capitan programmers. So far El Capitan has been the worst experience I have ever had with any releases of regular or beta versions of OS X. You should be ashamed of Mail. You should be ashamed of Messages which currently will not exchange messages with friends. Messages on my iPad works just find. You should be ashamed for producing new versions of programs with more bugs and less features than previous versions. You should be ashamed for designing an OS which blocks loyal and talented developers from updating their software. Why are you letting the experience of loyal users regress and then why do you ignore our complaints? Let's face it, the Mac is the only real computer Apple produces. iOS and OS Watch are distance cousins when compared to OS X. Why is El Capitan so poor? Sincerely, Jim PS: Note my signature below. I have a fairly quick i5 MacBook Pro and lightening fast, top of the line i7 iMac. I have tons of RAM and plenty of free, fast HD space. My hardware is not causing the problems.