Welcome to first stable release of React Native of 2019! There are a number of significant changes in this version, and we'd like to especially draw your attention to them:

Modernizing and stengthening flow types for core components
Breaking changes to ScrollView, CameraRollView, and SwipeableRow that make it no longer bound to the component instance in certain methods
Support for mutual TLS in WebKit
Asset serving from directories besides /assets
Numerous crash fixes and resolutions for unexpected behavior

Aside from those:

if you are an iOS developer, you'll need to manually link JavaScriptCore.framework when upgrading; this can be done via XCode, and following the steps shown here.
Android developers, please note that Android's target SDK 27 is supported. Work is still underway to land target SDK 28 support, and it will come soon.

Thanks to those who gave feedback on during the release candidate phase. If you're interested in helping evaluate our next release (0.59), subscribe to the dedicated issue here.

You can find the full 0.58.0 commit-by-commit history, plus the whole changelog over at react-native-releases.