ATMs in major towns. Credit cards accepted in some top-end hotels (especially in Addis), but in very few restaurants or even midrange hotels. Bring US dollars in cash.
Tips (gursha in Amharic) are considered a part of everyday life in Ethiopia, and help supplement often very low wages. The maxim ‘little but often’ is a good one, and even very small tips are greatly appreciated.
If a professional person helps you, it’s probably better to show your appreciation in other ways: shaking hands, exchanging names or an invitation to have a coffee and pastry are all local ways of expressing gratitude.
Furnishing yourself with a good wad of small notes – Birr1 and Birr5 – is a very good idea. You’ll need these for tips, taking photographs etc.