Can you cache a whole site [for snapshot purposes]?

A component to do that would be possible to write, yes.

Why do we need a PHP accelerator on 1.5?

There's a lot of procedural stuff in 1.0 code, so it would benefit less from an accelerator.

1.5 classes lend themselves better to caching - we've seen around 20% improvements using a cache/accelerator. The PHP accelerator works on PHP itself.

You don't have to have one, but it does improve performance.

Do template overrides include PHP logic?

Yes, they are PHP code.

The 'View' pushes data to a variable, and the layout formats it for display. So template over-rides can use logic such as 'foreach ($this->items) : ... '.

Technically the layouts break the traditional "rules" for a view, in that because it's php you can do damage to the parent application and data - but it's a tradeoff. Conversely patTemplate obeyed the rules, and the syntax is beautiful, but unfortunately has too heavy on performance and nested loops were a realy nightmare to implement.

Why hasn't the admin interface been re-written?

It has certainly been 'freshened'. Where 1.5 is a under-the-hood front end blitz, 1.6 will be an under-the-hood backend blitz - among other things.

Will sections and categories go?

Categories still require a section. The database schema does actually allow for infinite levels of category but Joomla! does not suport it natively - you could roll your own category editor in a custom component to take advantage of it though.

What happened with 'Summer of Code' ACL changes?

Not completely sure but 1.5 has simply been a matter of time and priority. There are two basic questions you ask with ACL. 'What can I do' - and that's actually not too hard to implement. 'What can i see' is a lot harder and we really need the Node Based approach that we've talked about for a while to address this.

Why not use ADODB for database drivers?

We found ADODB is to be a performance hog. It's only purpose was to help us use the phpGACL library natively - so rather than putting it on top of our existing "lite" db class, we fudged our db class with a rudimentary compatibility layer - which was a much lighter approach. It would be handy if a Postgres or MS-SQL server guru would step up and have a go and help write the db connect for it - and just see what breaks.

What's happening with ACL?

Joomla! ACL is based on a mongrelised version of PHPGACL library.
It's been upgraded to the full version and would technically allow for some improvements to be made with a custom component with far less "hacks" than we see at the moment for other systems on 1.0.

Does 1.5 address the issue with Itemids being 'lost' for content linked to in 'body'?

I.e. When you link in the body to content, sometimes the displayed modules disappear.

There is a default state that the system falls back on in an 'emergency'. It guesses the Itemid of the content item, but it may not be correct, particularly if the menu setup does not closely match the Section/Category setup.

You can't define which modules will be displayed within the link

[Follow up - the current trunk looks to be far better behaved now]

Can I bring a component across to 1.5 using PHPMyAdmin?

You may be able to, if you have legacy mode set in 1.5. No guarantees. The third party developers may have their own migration scripts.

Will my component migrate to 1.5?

You can turn Register Globals off in your (test database) for version 1.0.12 and see if your component still works. If it doesn't you definitely can't just port it over to 1.5