OK - it's 89' degrees today in Rome - and BEAUTIFUL. Everything is blooming and the smell of jasmine, honeysuckle, roses, etc. fills the air - NO PLACE I'd rather be than Italy in springtime!!
That said - I'm not looking forward to another summer without AC!
Regarding metro/bus/taxi service. Yes, the metro is limited by only 2 lines. If you're in Trastevere or over by Piazza Navona/Campo Fiori area there is no metro service. The A line is cleaner than the B line - but both are "effective." If your destination is near a metro line, that's always my first choice - especially in inclement weather!
I ride the busses every day I am not on a motorino. It's my primary method of public transportation and why I purchase a mensile (monthly pass). You can buy a local "bus map" with all the routes. Your "waiting" time will be substantially cut if you know alternative busses. For example, to get off the Cassia, where we currently live, I can ride either the 201,301,223, or 220 - rather than just waiting for ONE BUS! Like driving here, you have to know your destination by name, rather than a hwy #, etc., when riding the bus. It does take some practice - or do as I did, just ask other passengers (or when desperate, the driver!). The busses DO NOT run on the same schedule on Sundays and holidays... they are far less frequent.
Because we live here, we do not take taxis often. We see them as a "privilege" and to us, they are expensive - as opposed to the bus/metro! But after a late night - faced with a 1-hour bus ride, we will jump into a cab for the ride home (Next month we move DOWNTOWN!). Always go to a taxi stand and always use a registered taxi with a meter. At different times of the day the meter will "START" at different Euro amounts.
We do walk a lot - A LOT! And that's how we see Rome - but we always know where the closest bus or metro stop is... and we see that as our place to crash on the way home!
Good Luck,
Ciao,
Ron