Raised blood pressure, anxiety, insomnia, withdrawl symptoms without it, water retention (which leads to the higher blood pressure)-- but we're talking people who drink a fair bit.
Depending on a persons lifestyle caffiene is either a crutch or it isnt. Im out of the house for 10-12 hours a day and up pretty early, so it was a crutch for me. Granted I dont have the spring in my step that I used to in the mornings, but I feel better all around now that ive quit.
*I still drink 1-2 cups of a black tea during the day, but most of the time its herbal stuff or green teas.