I agree wholeheartedly with msorensson, I often actively avoid people who I recognise first. If we are currently friends then great but strangely have no desire to 'catch up' and go through the motions of small talk with people I haven't seen for years.
I hate seeing people from school, the whole '"how are you? what are you doing now? is that your girlfriend? what is her name? Hi Jane how are you? What do you do? Very good see you later" (Hopefully not)