So I've been using my Kindle 8.9" for about 2 weeks. I haven't had time to post some impressions so here they are:
The screen:
The screen is excellent. As good as any high end tablet, the only difference is the resolution doesn't exceed 1080p (but the tablet is also more than an inch smaller). The DPI is still retina and you can't see the pixels so really, it's like a smaller iPad. Excellent viewing angles and colors too.
The audio:
Amazon made a big deal about it and it's really good. Definitely the best tablet I've heard so far. You get loud, stereo sound which is rare in the tablet market market but it's actually good by reasonable standards. My sister who is not particularly tech savvy even remarked about it.
The battery:
I haven't done anything marathon with it but I'm charging it less than once a day. The battery life is very good.
The rest:
I'll echo thoughts about the buttons placement. They are very flush and hard to find. The tablet itself has no real orientation indicator save for the camera so you don't always notice which way you are holding it. It's small and solid, even more minimalistic than an iPad if that's possible. I haven't used anything that needs the camera so I can't comment on the quality. Everything else works like expected.
The software:
Probably the more interesting part. The hardware is easily the best bang for the buck but the software situation is odd. Most big apps for VOD and social networking at here and they have specific Kindle editions meaning they all work great. Outside that not all apps are available on Amazon and even if they are some aren't Kindle compatible (if you shop from the device it won't list incompatible apps). So Amazon has a Dropbox and Crunchyroll app but they don't work on Kindles it seems.
Sideloading is easy. I decided to install Chrome and Gmail because they're a little better than the stock. All you do is allow apps from unknown sources in settings, download the .apk and install using something like File Explorer ES (free in app store). No computer or rooting required (except to install Google Play proper), just remember to install the GoogleLoginServices.apk so you can log in. The hardest part is getting a hold of the apk you want.
The Kindle comes with some rudimentary software for documents, calendar, contacts, and email. They get the job done and that's about it. Silk is decent but Chrome I found had a few more features like incognito tabs and syncing to desktop that made it easier to work with. Speedwise they are similar enough but Chrome is a tad faster. Anyways you can pick your favorite and set it as the default no problem. Skype also comes loaded and it synced all my work contacts to my address book. Kinda annoying, I didn't want that.
The built in apps for video, music and books are as all excellent. They all hook into Amazon and behave much like their counterparts on Android and iOS except with added features like x-ray for movies. This is really where it shines, media experiences are great and they did a good job with the software.
The OS:
It works but it has quirks. I did not notice lagginess or strange pauses like reported so far. I'm mostly using Kindle optimized apps though so it can very well be poorly written apps that cause it. It takes a couple days to get used to the setup but as you become familiar with it you'll like it. My main problems are that there's no easy multi-task method. You need to go back to home and use the carousel to change apps which is kinda annoying. There's no quick menu you can open in an app. Also the keyboard is sometimes slow. I'm not sure I can install more languages unless I want to change language completely and there is no voice input option. Otherwise it works pretty well and categorizes your media by type. I think web should not be past the scroll edge because that's more useful but maybe people use this tablets differently.
Overall it feels like a small big tablet. While a Nexus 7 and iPad Mini are compromises for size, this feels like they took a 10" and shunk it as far as it could go. It's not small enough to really one hand but it's more manageable than a 10". Also get the case. The case is awesome, feels very nice and puts the kindle to sleep when you close it. It also holds it up in case you are watching a movie. Honestly I think this device is closer to what people need. The software needs to get a little better but it has everything it needs and/but nothing it doesn't. Very happy with it.