It seems as though I share my faith fairly often at times, but infrequently at other times.
I think it depends on what the occasion is. I am not a fan of injecting religion into conversations or situations that don't really open that door, but neither do I shy away from sharing my views--politely, of course--when other people present that opportunity to me.
As for the kinds of arguments people bring up, they can be almost anything, but if they're about the finer points of Christian doctrine (the nature of the Lord's Supper, for example), I usually don't feel like jumping in. There are differences between Christian denominations, after all, that aren't going to be resolved like that. Plus, this issue is complicated by the fact that what one person means by "share your faith" isn't what the next one thinks the expression means.