I have a Dell XPS 15 Touch with screen resolution of 3200 x 1800. PL-SQL Developer is ignoring Windows font sizing, causing menus, etc font to be real tiny and unreadable. I am using Windows 8.1 Pro.

This is indeed a known issue. Support for High DPI notebook screens is on the list of enhancement requests.

I am also hitting this problem (Lenovo Yoga 2). Is there a work around for this? I tried to change the font size in the settings, but the log on screen and the settings screen (have not checked others) are not really usable with larger fonts

The only workaround is to set the display resolution to 1600x900, but that is not what you bought this beautiful Lenovo ultrabook for of course.

I found something interesting: there is a version 1005.1713 available in the downloads (only the zipped exe). For me using that one solves the resolution problems.
Edit: Not really - as soon as the exe is trying to use to "normal" directory structure (with setup data, plugins etc) the resolution is again reverted to the unusable one

Marco, do you have any ETA for solving this issue?

No, we have not yet been able to address this.

I've just gone through the Windows option and taken the 2nd fix which makes the application usable once more:

http://windows.microsoft.com/en-us/windows-8/older-programs-compatible-version-windows