I am working on an attiny pcb. To protect the uC, I added a fuse in series with the power plug. (this one). But I am afraid 250ma will not be enough (if I want to power motors, etc.).
On the Uno schematic, (look if you want, you don't have to.) there is a 500ma fuse on the USBVCC to protect the computer, but there aren't any fuses on the regular 5V line. The only "fuse" if you will is that the regulator is 800ma Max.
The Attiny's have a max DC current of 200mA. So, do you think I should...
-leave out fuse al together?
-move fuse so that it is only in series with the uC, but not 5V out (but then other components can get shorted)?
-change to a new value (digikey has everything up to ~40A!)?
Why are you worried about protecting the microprocessor? Unless the microprocessor is damaged, it won't draw more than its rated current. If it is damaged, why bother protecting it?
As you said, the Arduino has a built-in fuse to help protect the computer it is attached to and not necessarily the Arduino or your project.
Keep in mind that most switching power supplies you might power your project with, probably have some form of short circuit protection already built-in.
Ask yourself two questions: what is the fuse going to protect and how would a fault occur?
For example, a PTC (like the one you linked to) may be a good option if you are using high capacity batteries. The fuse could prevent the batteries from going into a short-circuit condition, since most batteries do not have a current limiter. (Well up until they explode.)
Also you should understand that PTCs may be rated for a certain current, but that is generally when they start to open up. So a 250mA fuse may allow >400mA to flow before opening. You have to read the datasheet.