I might be a bit late to the ack game but holy shit its amazing. I had a huge app i needed to search for a class and make a quick edition every where. `grep -R` is great but then a friend told me to use ack and better yet `vim.ack`. I quickly grapped the plugin and installed it. Then ran `:Ack myclass` and boom a list of the files i needed to edit. Grep the plugin here
Ack also comes in a cli tool and can be installed with `brew install ack`
Im normally a Textmate guy but when i work in the terminal i always use vim. Ive known about MacVim for some time now but havnt really had any use for it as im living in Textmate. Yesterday i had to do some work on a server with a lot of editing files. While the terminal vim is great i got frustrated of not having my Textmate bundles and tweaks in vim. So i grapped a copy of MacVim at http://code.google.com/p/macvim/ and played around with it and got most of my bundles or equal awesome tools to do the same things.
Though i havnt been working that much in the terminal lately ive forgot a bunch of all the great features vim has. So i searched out for resources and the best one yet is http://vim.runpaint.org/ – they even have a twitter account at http://twitter.com/vimrecipes AND the book is available for forking at http://github.com/runpaint/vim-recipes
So go check it out! :)