To be honest, you should listen to what the guys are telling you here, if you hooked your 5V 100mA power supply for arguments sake to a LED it would not last very long, putting a current limiting resistor of about 300R / 330R will allow it to light up all happy!
I've seen loads of people put an LED as a power indicator forgetting the resistor and think their power section isn't working because the LED isn't on! Doh!
You need to look at the datasheets and see what the maximum per pin is AND maximum per device is that it can sink / source.
If you need to light up strings of LED's use transistors and drive the transistors using the micro / counter instead! (Don't forget the base current limiting resistor! 2.2k should suffice!).
I'm 29 and don't have anywhere near the level of skill set that most of the guys on this forum have, to which I will happily admit! I learnt with a 500 in 1 electronics kit and a book called The Art of Electronics, to which I still have for reference! I was programming windows and linux before uC's and have done so in basic, assembler and C, i've been dabbling with micros for about 3 years, and they still confuse me to this day, and always will I expect.
The thing about electronics is you are always learning, the thing about software is you are always learning, combine the two together, and you either accept that you will never know "everything" or give up trying!