Thanks for all the feedback Dmitry,

> One change I've noticed recently, is that the last few times I ran `M-x
> list-packages', it didn't display the "new" packages at the top.
>
> Might that be related to the recent changes?
>
Yes. I'm fixing it now.

>
>>    - For the sake of simplicity, when you hit `x' in the package-menu
>>    you
>>    will no longer get two separate prompts for install/delete. You'll be
>>    prompted a single time for everything.
>>
>>  I think "INSTALL (xxx-y.z) and DELETE (xxx-z.t)" is needlessly verbose.
>> It should probably be "Upgrade (xxx to z.t)", with maybe "and delete the
>> currently installed versions".
>>
>  I agree.

>
>>    - Most functions which involve downloading data now take an extra
>>    optional ASYNC argument (some of them also take an additional
>>    CALLBACK
>>    argument). This defaults to nil. If it is t, any downloads involved
>>    are
>>    performed asynchronously (and, if appropriate, CALLBACK is called
>>    afterwards).
>>
>>  Shouldn't there be some new tests?
>
> Yes. I'm still trying to figure out how to do async tests. Currently all
package.el tests use a local directory as the repository, but the async
functions only kick-in for remote repositories.
Should I use GNU Elpa for the tests? Might that cause hydra to unexpectedly
complain due to random connection issues?

> I have to say that package upgrading being only partially asynchronous
> looks perplexing. You say yes - it starts downloading stuff in the
> background - I can move around in the buffer, then suddenly the background
> process takes over in a synchronous fashion - I can't move cursor anymore
> and just watch some messages in the echo area. The Compile-Log only pops up
> at the end.
>
> While parallel downloading sounds good, maybe the overall interface should
> still be presented in a synchronous fashion.
>
I agree that's annoying and I have some similar plans. We can change the
package-installation logic to first download all files simultaneously, and
then unpack/compile all of them in the proper order. So large upgrades
would have a significant speed improvement.

>
>>    - Package downloads are performed in sequence, because it is
>>    generally
>>    not safe to do them in parallel
>>
>>  Why not? Simply downloading in parallel should be safe. Maybe not all
> at once, but 2-4 at a time, especially if they come from different
> archives, would be beneficial.
>
> I mis-expressed myself. Package downloads are safe in parallel, what makes
it non-trivial is that the subsequent unpacking/compiling needs to be done
in the right order (curently a package is installed as soon as its download
finishes).