1) ZIP uploads already implemented in version 3 2) This would be hard to implement. Instead, why not create one collection and just create your initial link in the website to navigate inside of that collection. User won't even notice. 3.) Choosable thumbnails for album/collection already in version 3 4.) Yes we need help writing documentation. I don't have time to do everything. 5.) PHP, MySQL, GD
Popeye, if you have some tolerance for minor bugs, version 3 (a developer release right now) offers most of what you want. I'm running it in my production server and have only experienced minor glitches that Mike is fixing as we find them. All in all, it's quite stable. You can find more information in this the official thread about version 3: http://www.plogger.org/forum/comments.php?DiscussionID=1095&page=1
I found that with v3's theme system you can separate the core script files from your theme styles to give you a lot more flexibility. This way you don't have to overwrite your hard work every time the program files get updated.
I recommend you give it a try!
As far as documentation, pre-requisites, and other information yes it's lacking. Perhaps this is something that some of the users could help contribute to. Popeye, do you want to create a thread that people can contribute to, to collect what are all the topics that it would need to address, what they found missing from the existing documentation?
A few years ago (...) you mentioned a kind of template tag similar to those used bij WordPress to achieve this: This would be hard to implement. Instead, why not create one collection and just create your initial link in the website to navigate inside of that collection. User won't even notice. At that time you said it was already functional. Any chance to have that in the final release?