Quote: "I've not looked into it, but are those formats easy to read/use?"
Well, the .mobi format is because there's Kindle Viewer for MAC and Windows:
http://www.amazon.com/gp/feature.html?ie=UTF8&docId=1000765261
It's cool coz you can emulate other devices!
Mobi is supported by the default app, "E-Book", on Android tabs (but the Moon+ Reader app, despite its few bugs, gives you a better experience as you can change the background image, colours, etc which is deal for night reading).
iOS also supports a .mobi app - prolly more than one, lol.
I don't know about Linux support though
but I'm sure there exists at least one decent Linux reader but have never looked into it. I also only use my "Reader" -- my tablet -- to read as I find my PC a little uncomfortable to hunch over (especially since my change to a laptop). My Kindle Previewer is really just for testing my books' appearance and formatting (stop testing appearance, finish editing and at least publish one!!!)
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So it's a fairly accessible format. The KindleGen app converts HTML/CSS into .mobi (although there are many tags and elements not supported but it's still fairly easy to compile your books if you ever want to publish anything. Mobi was definitely more supported when I last took a serious look into it.
I haven't looked into epub outside of my tablet but on my tablet it seems a more compatible format as far as the e-reader apps I tried go so my epub books often read better and seem to contain practically no format problems. I do blame the software more than either format though because .mobi's always look great on the Kindle Previewer, even when they get format-messed on my tablet. Perhaps there's a certain amount or responsibility to the people that compile them. Many people think KindleGen is a magic wand but one has to read the format specifications thoroughly and follow them correctly.
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"Quotes in signatures are just stupid, especially if you're quoting yourself" ~ me