One by one:
1.- Spreadsheets are hidden now, and will be back and more powerful soon
2.- Unused tags should be removed from the interface automatically after they are removed from all items and the interface is refreshed (i.e. F5 ). This will be improved shortly
3.- Sorry, but not yet. If anybody is willing to help, it would be great.
4.- We'll look at it, but I think the issue has been solved and will be available on next release
5.- It is not available yet, task templates are the only ones.
6.- Could be, how would you like it to work?
7.- This is a complete topic by itself (try searching for "filesystem vs db storage"). Very simplified: filesystem is faster, db has other advantages.
8.- We use linked objects instead of attachments. The mechanism is: Upload a file, write a message and after that you can link the message to the file. In general you can link any object with another.
Marcos