Overview of Changes in GTK+ 0.99.4:

* Reference counting revolution integrated.
  Refer to docs/refcounting.txt on this issue.
* Implementation of a decent debugging system, you would want
  to export GTK_DEBUG=objects if you are going to develop gtk applications,
  refer to docs/debugging.txt for further information.
* Additions on the signal code for querying information about certain signals,
  and pending handlers of signals.
* Support for user signals, and major changes to internal signal handler
  handling for proper signal removal and invokation of after signals.
* Additional signals for various widgets e.g, GtkHandleBox::child_attached,
  GtkHandleBox::child_detached, GtkWidget::style_set, GtkWidget::parent_set.
* GtkTooltips became a true descendant of GtkObject via derivation from
  GtkData and facilitates an extra tip string which can be used as e.g. an
  index into context help.
* Split up of the widget/object flags into a private and a public portion,
  consult docs/widget_system.txt on this.
* Support for hot keys on gtk programs via gtk_key_snooper_install().
* Reimplementation of the *_interp functions as *_full functions to provide
  simple callback functions as well.
* Idle functions are now prioritized.
* Many enhancements to GtkNotebook.
* New widget GtkSpinButton, check out testgtk.
* New widget GtkTipsQuery for letting the user query tooltips of widgets.
* Addition of GtkEditable base widget to encapsulate selection and
  clipboard handling. (GtkEntry and GtkText use this)
* Text widget more complete.
* Additions to GtkStatusBar to make it complete.
* Gdk now supports regions.
* Access masks for widget arguments (GTK_ARG_READABLE/GTK_ARG_WRITABLE).
* Function replacements:
  g_string_hash() -> g_str_hash()
  g_string_equal() -> g_str_equal()
  gtk_tooltips_set_tips() -> gtk_tooltips_set_tip()
* Support for quit handlers in gtk_main().
* Motif window mangaer hints support.
* Widget arguments are now flagged for readability/writability.
* Additions to documentation.
* Various FAQ updates. (FAQ now included)
* Clean ups and many many bug fixes by a lot of people all over the place.
* New, long and descriptive ChangeLog entries for bored readers ;)

Overview of Changes in GTK+ 0.99.3:

* Filesel enhancement / stability changes
* New widget, gtkcombo 
* Widgets in the toolbar do not get the focus
* New widget, gtkstatusbar (still in-progress)
* g_string_equal renamed g_str_equal
* g_string_hash renamed g_str_hash
* new gtkbox functions to allow modification of the child 
  linkage after the widget tree is setup
* gtk_*_get_arg() and gtk_*_set_arg() fixes and implementations
* DND changes/fixes
* Entry widget now has set_max_length function
* Handlebox widget changes/fixes 
* Some work on text widget (still in-progress)
* Now the toolbar supports arbitrary widgets as well
* CList has resizable columns again
* CList now looks consistant with scrolled windows
* Remove flickering from entry widget
* Added switch_page signal to notebook widget
* Documentation additions
* Other bug fixes...