Sorry, yes. I can address some of your questions. I have a couple of android phones and a couple more devices as well as two WP7 phones. I'll answer your ebook question for each.
Ebooks---
Android: I use Calibre as my ebook management software. It has the ability to launch a server (OPDS server). It's an extremely popular piece of software and there is an Android app called Calibre Library ($5) which allows you to connect to that OPDS server and download books. If you screw around with it enough, you can get it to automatically download the book to a directory of your choice and ebooks apps like the Nook app or Moon Reader can automatically pick up the book and you can start reading. It works.
WP7: Much easier to use, in a lot of ways, but fewer options in the app store. A couple of notable ones are Freda or ABookReader. Both connect to your dropbox account and you just pick the book you want to read. Freda also can connect to the Calibre OPDS server and you can search/download books that way. The dropbox thing is dead simple, however and works very well. I prefer this, as it is completely cross-platform and I don't have to spend 1-2 hours every times I reset my Android device trying to figure out why books don't seem to get picked up.
It sounds like Flash is pretty important to you; in that case you are probably better on Android since it's really the only mobile solution with Flash. In reading how your need for flash is alleviated by apps, it comes to mind that one neat thing that WP7 does (Android can, as well, but it works less frequently) is that, when you go to a website with an associated app on your phone, it pops up a thing suggesting you run the app. BBS websites are particularly good at this....
You can not change program defaults in WP7. There are reasons for this- some of the Android malware operates by changing the default apps to non-safe applications. An example I read of this involves changing the default browser to an identical browser with a keylogger. Somewhat problematic. Moreover, the whole idea of "Apps" is less strong in WP7 than it is in Android or iOS- deep integration is more the key here. For example, instead of taking a picture, exiting the camera app, going to the app list, finding a picture editor, launching it, then picking a photo, editing it and saving it as you would in Android, WP7 performs the same operation like this: take a picture, and, while looking at that just-taken photo, hit extras and immediately launch the picture editor you want. The OS is intelligent enough to know which apps should associate with certain types of files.
Podcasts----
I don't know the exact state of Zune on the Mac, but in WP7 a PC is really rarely needed. I think the app you'd want is BringCast. Supports streaming and (maybe?) downloading podcasts. However, this is assuming that you can't find the podcast in the mobile Zune marketplace. If it's listed there, you don't have to worry at all- you just subscribe to the podcast from the marketplace and it will automatically download everytime you are on WiFi. You can also set this to download even when you are on 3G, but that's not enabled by default to save on your data connection.
Overall---
For a hobby device, I enjoy Android. I put on custom ROMs, hack it, don't worry about updates. It's fun. I just wouldn't want to rely on it. My Samsung Captivate is still lacking the latest updates, and don't even get me started on why my HTC won't update without losing half of the reasons I bought the phone in the first place.
WP7 is polished. Much more so than Android, and the UI is excellently thought out. It's more limited, definitely, but I don't mind some of the walled garden approach when I get these things in return: safe apps, apps that work consistently, ease of use, decent hardware. I don't get the first 3 on Android. And (this is a real thing) I don't have to worry about the Android malware that was discovered recording calls and sending them back to the malware writers.
Conclusion---
If flash is that important, you'll need to stick with Android. It's really the only thing there that will do it. If not, there are reasons on both sides to go with each. Power-user vs Ease of Use/Elegance/Simplicity is a start, but with Power-user you'll need to remember there is a corresponding increase in micromanagement. F
Feel free to ask any questions, I'll try to answer what I can.
But that is simplicity and it falls under the "just works" mantra. When the system can see what's installed and assign a new file format to that without leaving you wondering what to do. That's "just works" at it's best. The file opens merely by selecting it and you don't have to think about how to open it.
It's funny that android has flash because I need it less on that platform than others because it associates the correct app with the correct file/link(not 100% of the time, but enough, almost).
Honestly, it boggles my mind that i've been asking on both android and WP7 forums, several of them, about how to put ebooks on their perspective devices and nobody knows how. Does nobody read books? I've started with ebooks on my dell axim back in 2003 and have been using them ever since. So getting my own ebooks on my device is kind of a big deal. I know how to do it on android now, not as easy as ios but it works. Still waiting on how to do it on WP7.
While I do have an android phone I still have time to return it if WP7 is compelling enough but as of yet I haven't figured out how to do the things I want to do with it.