Here is a quick rundown of some of the changes in Beta 5 posted today. For the full details as always check out the release notes

• Structs and classes can conform to ErrorType
• Non-failable initializers can now chain to failable initializers by using !
• Debug builds should have better performance due to using pre-specialized generics in the standard library
• Generic subclasses of Objective-C classes are no longer exposed in the bridging header
• Dictionary's removeAtIndex returns a key-value tuple (matching Ar
• @NSManaged can now be used with methods and properties so you can deal with the automatically generated KVC accessors
• You can now reflect on enum instances to get the current case if the enum has a payload; there will be one child where the label is the case name and the value is a tuple containing the payload. Unfortunately to handle a case without a payload you can't use the mirror (use String interpolation instead), nor can you get a list of the enum cases by reflecting the type.

Standard Library

• SequenceType adds forEach to let you apply a function to each element
• SIMD integer vectors only support the unchecked operators (because that's how the underlying hardware works in most cases anyway). For those who may have forgotten, operators like &+ or &- are not checked for overflow or underflow.
• The confusing Word and UWord types were removed; just use Int and UInt.

Resolved Bugs

• The Swift migrator doesn't generate spurious build errors
• The full documentation for the Swift standard library is now shown in Xcode (yay!)
• Changing the body of a function should no longer trigger rebuilding of dependencies; this should speed up builds by a decent amount in many cases
• The ambiguous "Type checker diagnostics continue to improve in precision and specificity". I have no idea how extensive this is yet.
• The compiler no longer crashes when a generic struct contains a weak or unowned reference

Still Bugs or New Bugs

• LLDB enforces try which is not intentional
• Use of guard let at the top level of a playground or script may result in memory corruption(!); this bug gets an explicit "will be fixed before release" mention.