Atomic increments allow you to avoid problems with a concurrent access to a counter: http://www.alfreddd.com/2011/01/atomic-increment-in-rails.html
Install:
gem install rails_atomic_increment
Usage:
user = User.first
user.account_balance # => 100
user.atomic_increment!(:account_balance, 2)
user.account_balance # => 102
user.atomic_increment!('account_balance', 2, :reload) # reloads from DB
user.account_balance # could be > 104 if it was updated by another process
user.login_attempts # => 7
user.page_views # => 1000
user.increment_counters!([:login_attempts, :page_views]
user.login_attempts # => 8
user.page_views # => 1001
Copyright (c) 2011 Josh Shupack