I had a SS3 site I was developing.. then a core change caused it to break (think it was about private statics?)
Anyway, today I decided to get back to it, but after trying to update with composer..
I gave up stripped out all modules, edited the json file, and then required them again via composer, thinking that forcing the latest versions would fix any issue.
Alas... I now get this error if I try to view the site (front or admin)

"Notice: Undefined index: configDirs in F:\vhost\mysite\framework\core\manifest\ClassManifest.php on line 133

Fatal error: Access level to BlogEntry::$db must be public (as in class Page) in F:\vhost\mysite\blog\code\BlogEntry.php on line 7"

Please help..

Fatal error: Access level to BlogEntry::$db must be public (as in class Page) in F:\vhost\mysite\blog\code\BlogEntry.php on line 7"

You'll also need to downgrade the blog module to an older version (the public -> private change is unavoidable) though I recommend you get everything on 3.1 and fresh as 3.1 has a lot of solid improvements so work the short term pain.

OK, I have a running copy again.. WOW.. a bit of a learning curve to this git + composer thing..
so, my json file now reads:
{
"name": "silverstripe/installer",
"description": "The SilverStripe Framework Installer",
"require": {
"php": ">=5.3.2",
"silverstripe/cms": "3.1.x-dev",
"silverstripe/framework": "3.1.x-dev",
"silverstripe-themes/simple": "*",
"silverstripe/blog": "dev-master",
"silverstripe/comments": "dev-master",
"silverstripe/widgets": "dev-master"
},
"config": {
"process-timeout": 600
},
"minimum-stability": "dev"
}

It works but I am unsure if this will update correctly overtime?
Also the suggested instal of simplepie, where can it be found and how to install?