The SDK Manager in Tools r9 will have a slightly different installation mechanism for packages, which I hope should fix part of issue 4410. This is mostly for Windows users who have trouble updating packages and get the infamous "folder failed to be renamed" error. (If you want technical details, there's a pretty good description of the fix in the changeset, so I won't paraphrase it here.)
There's still one known issue not addressed: the SDK Manager fails to upgrade a platform from within Eclipse when there's a layout editor using that platform. Some files are locked by Eclipse. We should be able to address it in the next version.
Another thing fixed for the SDK Manager in Tools r9 is the support for "broken" add-ons. If you currently install an add-on from a third party (e.g. Samsung's Galaxy Tab add-on or Sony Ericsson Xperia X10 add-on) and you lack the platform it was based on (e.g. Android 4 "Donut" for the X10), you won't see the add-on and there's no error or any kind of message indicating you why. Oops :-) Well now, not only you can see the "broken" add-on in the Installed Package list, but if you update you'll automatically get the platform that would fix the add-on: