save this as `.git/hooks/post-merge` in any of your repos. Then, when you do a `git pull` (or really any merge I think), if any migrations were updated or the Gemfile was edited, you'll get a handy reminder to migrate or bundle install.

post-merge

#!/usr/bin/env ruby

# Put me in .git/hooks/post-merge
# Then do chmod a+x .git/hooks/post-merge

migrations = `git diff --name-only master master@{1} | grep db/migrate | wc -l`.strip.to_i
if migrations > 0
  puts " "
  puts "**************************************************************"
  puts "**************************************************************"
  if migrations > 1
    puts "You just pulled changes that included #{migrations} database migrations."
  else
    puts "You just pulled changes that included a database migration."
  end
  puts "You should run `rake db:migrate` and `rake db:test:prepare`."
  puts " "
end

gems = `git diff --name-only master master@{1} | grep Gemfile | wc -l`.strip.to_i
if gems > 0
  puts "**************************************************************"
  puts "**************************************************************"
  puts "You just pulled changes that included an updated Gemfile."
  puts "You should run `bundle install` to get the latest gems."
  puts " "
end

rake db:migrate && rake db:test:prepare is handy for copy/paste