It's been a little over two weeks since Apple cracked open the iOS 8 beta to anyone with an Apple ID and a spare device, instead of making you pay the $99 developer tax to get early builds. I signed up the day the profile went live, downloaded it that night, and put it on the phone I use every day like an idiot. Don't do that. I'm going to tell you how to do this properly, and also complain for a while, because that's basically what this blog is for.
First, the actual how-to part
If you want in: go to beta.apple.com, sign in with your Apple ID, and it walks you through installing a configuration profile on your device. That profile is what unlocks the OTA update to the beta build in Settings > General > Software Update. It's genuinely simple, way simpler than it used to be when you needed a developer account and a UDID and some registered-device voodoo.
Two things before you touch that button, though. One: back up with iTunes first, a real local backup, not just iCloud. You cannot downgrade from iOS 8 back to iOS 7 by restoring an iCloud backup once you've gone forward, and Apple doesn't sign the old firmware once a new one ships, so if you get stuck you are stuck on beta software with no way out except restoring from that iTunes backup you didn't make. I learned this from a forum post at 1am, not from personal disaster, but only barely. Two: use a phone that isn't the one your life runs on. I put it on my main 5s and spent the following week explaining to people why I hadn't texted back, because Messages was dropping notifications about a third of the time.
What's actually different, in no particular order
The predictive keyboard thing (QuickType, they're calling it) is the feature I notice the most, honestly more than I expected to. It sits a row of word suggestions above the keyboard and they're context aware in a way autocorrect never bothered to be. It's not perfect, it still occasionally suggests a word so far from what I typed that I wonder what it thinks I'm trying to say, but for everyday texting it saves real time.
Interactive notifications are the other one I keep noticing, mostly because I keep forgetting they exist and then being pleasantly surprised. You can reply to a text from the lock screen now without fully opening the app. Small thing. Adds up over a day of picking your phone up forty times.
Health app is there but it's basically empty right now, just a shell waiting for something to plug into it. I opened it once, looked at the blank graphs, and closed it. I assume this matters more once actual hardware and third-party apps start feeding it data, which is presumably the whole point, but as of today it's a placeholder.
The stuff that's broken, because it's a beta
Battery life is noticeably worse. Not dramatically, but I'm charging around dinner time instead of coasting to 11pm like I used to. Instagram has crashed on me more times than I can count, closes itself the second I try to post a photo, which is annoying but not exactly a shock for a beta build two weeks old. Tweetbot's beta build has similar issues, freezes on refresh sometimes and I have to force close it. iCloud Drive is switched on in Settings but doesn't actually do much of anything useful yet, since none of the apps on my Mac (still on Mavericks over here, no Yosemite beta for me, I'm not that reckless) know what to do with it.
None of this is really a complaint about Apple's beta, to be clear. That's what a beta is. My actual complaint is more that I keep forgetting I'm running unfinished software and get irrationally annoyed when unfinished software acts unfinished. That one's on me.
If you're the kind of person who reads changelogs for fun, or you just want a preview of what your phone is going to feel like in September, it's worth putting on a secondary device if you've got one lying around. A backup iPhone 4S has been earning its keep in my drawer for exactly this reason, and it's now running iOS 8 while I go back to being a sane, cautious person on my actual phone.