Since I am retarded and afraid of taking the bus here, I either walk, bum rides from friends or take taxis. Here is a brief summary of what I've experienced in taking taxis pretty regularly around Mendoza. The good, the bad, and the ugly... on 4 wheels.
Taxis here are cheap. The base fare is about 4 pesos (maybe $4.50) during the day and about 5 and change after midnight. Basically, most of my taxi rides around centro have been $10-15 pesos (or $2.50 to $3.75).
On the whole, most of my taxi-cab experiences have been quite good here. Some of the drivers are pretty young and hip, and try to speak English to me even if I'm speaking to them in Spanish, asking where I'm from, telling me they know someone in Texas, etc. And nearly every single male driver I've had that drops me off at my apartment after dark waits for me to get in the door before they drive off. It's something I'm grateful for, and it's them going out of their way to make sure this gringa is safe on their watch.
The drivers are sometimes crusty men in their 40s who talk very little, drive a little too fast, and rebuff any attempts at friendly conversation. But they don't normally overcharge or try to screw me over because I'm a gringa. Me gusta mucho.
The worst experiences I've had here are very few and far between. One was last week, when taking a cab back to my apartment, I got in and gave the driver my address. He nodded, and we were off. We got to my neighborhood, and he missed a turn. I was going to say something, when he pulled over a few blocks later next to another cab driver to ask where my address was. He never asked ME where it was, and took me five minutes out of the way. I told him I knew where I lived and could direct him. Then, finally, when we arrived at my apartment, he made me pay the full fare. Dickhead.
Then I had a woman driver last night. Now, I'm a girl. I am a girl who can drive. Usually, I don't find many women to be good drivers. Sorry, it's true. This woman was no exception. She was rude, abrupt, and drove erratically. She also didn't tell me she didn't know exactly where I lived until we turned down a street near my apartment (that was a wrong turn, since the streets are mostly one-ways and she turned too soon, and would have to loop around to get in front of my apartment) and I made her let me out on the corner. No sooner had I paid her and shut the door did she speed off in search of other customers to be a bitch to. She wasn't about to wait around to make sure I didn't get raped or anything walking by the abandoned, dark construction site. Gracias.
There are also taxis you can order, called a remise. They come in handy on Sundays when there are less people around and less taxis available to be hailed on the street.