I'm developing a site with SS3 . The site and the admin area are really slow.

I'm also worried what will happen when a realistic amount of data is loaded in, rather than the 15 pages or so i have added to test.

Running page speed analysis, it gets 0. I haven't seen that before so i ran it a few times : )

It takes around 3 seconds to go from a list view to an edit screen in the admin area.

adding in all the htaccess performance wizadry from html5 boilerplate increases page speed score but dosn't really speed things up much. whilst i think it would be a good idea, i don't think minifying the admin area css / js is going to make much difference either, as the core issue is the server response time.

I'm on php5.4, osx, mamp pro, mysql and have 512mb of memory allocated to it. So things are only going to get worse when i upload it to the little vps in the sky.

ill upgrade to 3.1 (its not stable yet, but worth a shot i think) and see if that improves anything.

Make sure you have a PHP cache running, APC or XCache make running it a decent % faster.

Also make sure you don't have anything that flushes the cache in your _config.php. Some developers liked the 'handiness' of always flushing while in dev but now the framework's manifest is much larger so flushing has a much more negative issue on performance.

I have noticed that SilverStripe can sometimes be slower on MAMP - especially on my MacBook :) - then on most (good) production servers

Also you do need to check speed issues in live mode only, since dev mode issues can slow things down dramatically (working on a site using Less, I found dev mode being 4 times slower then live on MAMP)!

In dev mode, it looks like template changes do not need to be flushed at all (aside from sometimes email templates and other such stuff) so I suppose there's something going on with the manifest as well..?

I don't suppose the CMS will ever be lightning fast, but that doesn't have to be the same for the frontend. You might want to look into partial and/or static caching as well...