(actually, they haven't been asked of me frequently, but they should be)
The best place I know of for more in-depth answers to these questions is Ray Comfort's book "The Way of the Master". However, here are some short answers off the top of my head...
1. You don’t seem to be winning many people to the Lord. Is this a waste of time?
I definitely see my role as "planting seeds" rather than winning souls. "The wind blows wherever it pleases. You hear its sound, but you cannot tell where it comes from or where it is going. So it is with everyone born of the Spirit". (John 3:8) It is the Holy Spirit who brings spiritual rebirth, and I am just honored that I could play a role in the process. Because of this I don't feel the need to make any emotional appeals or use any sort of manipulation. I can just obediently share what the Bible says and relax and pray that God will do the work of heart transformation that only He can do.
2. "Do you lead anyone in a “sinners prayer” and assure them that they are saved?"
Leading someone in a "sinners prayer" could very easily be a form of manipulation. If they are truly experiencing rebirth and the deep conviction and repentance that comes with it, they won't have to be led in prayer, they will know what to say to God. If they want help I may try to help them understand what an appropriate response would be to the awesomeness and holiness of who God is and what He has done in their life, but the response needs to be their own. The worst thing I could do is assure a person of their salvation when in fact they aren't really saved, and there is no way for me to know. I do tell others that they need to test themselves to see if they are in the faith, and the fruits of repentance will be evidence of a truly saving faith.
3. "Do you follow up with these people?"
I give those who seem interested a personal summary of the Gospel along with my cell phone number, my e-mail address, and my church address and website. Out of several hundred of these given out, no one has ever contacted me, which surprises and saddens me. I'm not quite sure what to think about it. My guess is that, regardless of my friendly and conversational approach, anyone who evangelizes like this in our culture is seen as an extremist (though biblically this is simply what we as Christians are expected to do) and if a seeker wants to learn more there are usually "safer" Christians in their life to talk to. I give them my info and don't ask for theirs in return to emphasize that it is their responsibility to respond. I am dedicated to follow-up and discipleship within my local church, and for me to chase after people who show initial interest would severely take away from the time I spend in both street evangelism and church discipleship.
4. Statistics show that few people in our culture are led to Christ by direct evangelism. Shouldn’t you focus on building relationships?
I believe that so few people have come to faith in Christ through direct evangelism in our culture not because it is ineffective, but because relatively few people are doing it. Even if no one is blessed by my efforts, I myself have grown so much in my faith and ability to share my faith that it is totally worth it to me. The people I know and love and am in an ongoing relationship also benefit from my efforts at evangelizing strangers because I've become better able to clearly explain the Gospel to everyone.
5. "What do you do when people bring up intellectual arguments like evolution or refer to other religions?"
I have studied these areas a lot and am able to bring a lot of sense to a conversation about them. I talk about them for a while depending on the circumstances because I want people to know we don't have to live in denial of these issues. However, most people use these arguments as a smokescreen to cover up their pride and love of sin, and when I ask if they would be found to be a "good person" if there is indeed a Judgment Day these intellectual arguments usually become unimportant. What is more important to most people is that they want to keep their "trump card" - their idea that they are a good person worthy of heaven - just in case they find out in the end that there IS a God and the Bible IS true.