First: thanx for an excellent piece of software!
Second: When I write, I often use parts of other texts I’ve written, copying/pasting them back and forth. In this, fonts tend to get messy, they vary in size etc. I could of course use “Paste and match style”, but this I constantly tend to forget. Is there a way of making Scrivener constantly display all text in a certain font, esp in full screen mode (which is the heaven of writing, btw)?
Documents>Convert>Formatting to Default Text Style. You can select multiple documents at once and run this command to adjust the font, indentation, etc. to your global defaults set in Scrivener>Preferences:Formatting (or to the project defaults, if you set something different in Project>Text Preferences…). When you select the menu option, it will give you a chance to limit the scope of the conversion, so take a look at that before you click okay–if you have anything you’ve copied in that needs special formatting (tables or lists, for instance) you’ll probably want to check some of the boxes. In a pinch you can just convert the font.
Also make sure that your default font has options for italics and bold if any of your text uses that–converting to Lucida Grande, for instance, which doesn’t have an italic option, will make you lose all the italics in your document. You can check by opening the font palette and viewing the Typeface list for your selected font family.
Thanks, that helped my bricolage-like situation! Is there any way of making this happen automatically for an entire project? This in order to avoid having to do it over & over again, after I’ve messed things up, which I most likely will?
I don’t think there is. I’m having to do it all the time, as I’m importing documents from Word and it’s much easier to drag them in than copying and pasting, especially as they can be rather long. I have set a key shortcut for that menu entry (Ctrl-Cmd H, in my case … I used to use Ctrl-Cmd D with version 1.x, but now that Dictionary is more hidden, I keep the latter default for that.) Makes “Convert to Default Text Style” totally painless!
I drag a text in, take a snapshot, then Ctrl-Cmd H … and start editing.
Mark
Thanks for the tip, implementation in progress 
While you can’t do it automatically, you can select several hundred files in the binder and run this command on them all at once. Another trick, once you get the scope of the changes adjusted to the way you prefer, you can hold down the Option key when calling this menu item to skip the options dialogue.