Most tourist businesses, including lower to midrange hotels, accept cash only. ATMs are widespread in major towns, but surprisingly hard to find around Lake Ohrid except in Ohrid town itself.
Macedonia's national currency is the denar (MKD), but many tourist-related prices (such as transport and hotel costs) are quoted in euros – you may even find that the business owner doesn't immediately know the denar price if you ask for it. Hence Lonely Planet lists prices as they are quoted rather than in denars only.
Carrying some euros into Macedonia can be handy for larger outgoings such as hotel bills, but note that it usually works out better if you pay for smaller costs in denars. Motorway tolls, for example, are about 30% more expensive if you pay in euros.
Taxi drivers hate it when you pay with a 1000-denar note, and may make you go into a shop to get change.
Macedonian exchange offices (menuvačnici) work commission-free. ATMs are widespread. Credit cards can often be used in larger cities (especially in restaurants), but you can't really rely on them outside Skopje. Avoid travellers cheques altogether.
Macedonia doesn't have a tipping culture except at restaurants, where 10% is the norm.