You can try to use Wowza Media Server stream to Web/iOS/set-top-box clients. Your Pi just will encode video from raspicam and send to Wowza Server via RTMP as FLV container. This command will send Pi's camera stream to Wowza with some parameters and it should work without problem.
raspivid -o - -t 99999 -hf -w 640 -h 360 -fps 25| ffmpeg -i - -re -deinterlace -s 360x288 -acodec libfaac -ar 48000 -ac 1 -ab 64k -vcodec libx264 -vpre normal -f flv rtmp://yourstreamserver/live/streamName
In amazon EC2 you can create a Wowza instance and test Wowza Server. Your customer/spectator count depends on CPU power of EC2 instance.
I worked RTMP Streaming with Wowza for years, it fits your request, but i don't guarantee RPi side.