This is what I deal with most of the time on the support channel:
1) bitcoind is installed in a non standard folder. You need to point that to Armory in the File -> Settings menu. On Windows, in the current version, you have to point at the folder containing the daemon (bitcoind.exe), not just the top Bitcoin installation folder. This bug will be fixed in 0.91
2) The blockchain is in a non standard folder. This is an issue regardless of bitcoind (auto managed) or BitcoinQt (no management). You need to point Armory to the raw blockchain files, either through the Files -> Settings menu, or by using the --satoshi-datadir command line argument
3) Some users have modified bitcoin.conf, usually to reduce connectivity. Armory connects as a node so bitcoind needs to allow it in. The common approach is to add listen=1 in bitcoin.conf. I prefer bind=127.0.0.1. Worst case scenario, getting rid of the .conf (rename it to something else for instance) fixes the issue.
Note that in auto manage, Armory tries to query bitcoind status through the JSON-RPC API, and it sets its own log/password in bitcoin.conf for that purpose.
4) "It's been sitting here for hours synchronizing". By far the most annoying state to fix, since I have personally never ran into it, and I have sync'ed the blockchain and Armory's DB from scratch quite a few times. Same goes with the other devs, we just don't run into these, so we don't really get to observe the bug.
There are 5 cases essentially:
4.a) Some users just don't realize how long it takes to download and verify the blockchain. Thats 10-20% of the user base.
4.b) A certain amount of users (can't really give you figure because they get mixed with case 4.d) do not properly set their system clock, resulting in bitcoind never fully syncing with the network.
4.c) Syncing Armory without a wallet loaded. Don't do that. Create a mock wallet if you have to.
4.d) Corrupt DB. Armory's DB somehow got corrupted. Most users experience an Armory freeze and/or crash when it runs into the corrupt data. At this point start Armory in offline mode (use the --offline command line argument) and click on Help -> Rebuild and Rescan Databases. If Armory still crashes, you have to manually delete the databases folder in Armory's datadir. I'd say 10% of our users run into this.
4.e) Messed up blockchain. This is our main concern currently. Even though bitcoind reads the raw files properly, Armory chokes on them somewhere. Our issue is that we never got a blockchain in that state to observe the issue, so we haven't gotten around fixing it. We have yet to find someone willing to upload 14GB worth of blockchain to us either =P. At any rate, the solution to this issue is to delete the blockchain raw files and let bitcoind resync. About 10-15% of our user base runs into this.
Thanks! I'll get one of my writers on this right away.
I'm currently finishing up the offline tutorials, then I have to add some videos.
I'll add a common problems section for this after that, so you can just refer users to the guides.
If have any more common problems and solutions just add them to the topic and they will be added to the roadmap