1. Google Doc
Column A and B - Name - Columns for First and Last so I can sort easily
Column C - Priority - Based on Keith Ferrazzi's A/B/C guidance, I enter the frequency (in weeks) that they should be contacted. For A contacts, it's 2, 6 for B and 12 for C.
Column D - Last Contact Date - I update this every day or two when I have had an interaction with people.
Column E - Next Contact Due - =Column D + 7*(Column C)
Column F - Overdue? if(Column E > Today's Date,1,0)
Format Column F to turn yellow if the value is 1.
Column G - Mention - here I put a note about whatever I need to mention or ask about next time.
2. iPhone - I save this page as a bookmark on my homepage so I can update info on the train or look for people who are overdue. Quick comment on Facebook or Twitter, invite to coffee, comment on their blog, etc. and I'm done.