Grumpy_Mike:
OK to actually answer the question, I would say the dividing line is about 400 to 500mA when switching over to a FET, but it isnot hard and fast.
That's also the figure I use, when using breadboard or stripboard. For PCB designs I use mosfets below 400mA too - there are lots of inexpensive medium-current mosfets that are only available in SMD packages.