The bus system is very problematic for a tourist. The guidebooks emphasise that you must buy a ticket (flat-rate of 1€ for 75 minutes travel) and validate it on board. But we hardly ever saw locals validating tickets and there seems no way of checking, apart from spot-checks by (non-existent) inspectors. The truth is that for most routes in the centre, particularly at rush-hour, the buses are impossibly crowded so there is only a slim chance of getting onto a bus and no chance of getting near a validating machine – ticket revenue for ATAC must be tiny for the number of passengers carried. Furthermore ATAC has clearly decided not to put a diagram of the route inside the bus or to have a screen telling you what the next stop is. This adds up to a really tourist-hostile service.
Google map: bit.ly/dOTiNm
Well, mainly true but perhaps not a good tip for newcomers to Rome. Be careful with inspectors! ATAC and the Italian railways are cheap enough, with the "Airport Surcharge" as the only real rip-off, so why not enjoy some stress-free travel in such a wonderful city? And if you like buses, then buy one of the cheap bus maps at a kiosk (the routes are staying much the same these days) and enjoy the wait for the next bus by studying Romans? They are rarely "tourist hostile", they care for their city ... I agree. Sad to say but the ticket machines mostly steal your money as well. I advise walking or risk getting caught. I was caught on the underground having forgotten to vaildate on what I thought were broken entry gates. Good news is that you show your passport and then just give them an address and they send the fine to that address :-)
Is this your business?