Several of the comboboxes that I use regularly (the box to select syntax highlighting in the gedit statusbar, boxes for choosing smart playlist criteria in Banshee, etc) require me to click on them with the mouse, scroll down for awhile, then click on the item that I want. Being able to type into these boxes and have the list jump to the first matching entry would be a nice time saver.
So I'm wondering, has this been implemented in Gtk+ 3? If not, is there a bug report somewhere that I could subscribe to? And is there a technical reason that this hasn't been implemented, or is it a design decision. Since this behavior is common in all major web browsers, I'm sure I'm not the first person to think of this, but a few minutes of Googling didn't lead me to anything relevant.
No, this hasn't changed in gtk+ 3.
Back in 2001, a bug was reported that dropdown comboboxes couldn't be navigated using the keyboard (even the arrow keys and Enter). All parts of this bug were fixed except the part about typing text while the combobox has focus and having the list select the correct item alphabetically.
More recently, a new bug was filed requesting that combobox lists respond to all keyboard input by selecting items alphabetically. This issue is still open.
Well, the syntax box in Gedit isn't a combobox, just a button with a popup menu. The Banshee boxes are regular comboboxes, not comboboxes with entries.
So to answer your question, GTK 3 does have combobox entries, just like GTK 2. But the developers of each application choose wether to use them or not, same goes for any other widget. If a developer thinks a combobox is more convenient than a comboboxentry, then that's what you get.