I only ever ask for a ride to and from the metro if I'm in the burbs. Personally, I would only offer rides to people if they were on my way. I also usually decline offers of rides from people if taking me home or whatever is way out of their way. I'm a grownup, I can get myself around town on my own.

There are a few notable exceptions, like asking a pal for a ride to and from the hospital. But I would need that even if I had my own car.