Apple's latest Mac OSX release, 10.5, dubbed "Leopard", does a great job to remedy the problem Rails developers had with previous releases - Ruby is now installed and works correctly, with Rails and a whole bunch of other common gems installed too. Awesome stuff.
Firefox has Firebug, the best JavaScript debugger on the face of the planet. The developers came up with a subset of Firebug that works on all web browers, creatively named Firebug Lite and should be an essential part of any web developers toolkit.
Quick tip - if you're just using ImageMagick to get dimensions of images, try using image_size instead, it's written in Ruby, works well, and installs really quickly, rather than the five years it seems rmagick to compile & install.
I've just wasted several hours due to what turned out to be a bug in the current Safari 3 beta (on OSX Tiger). If you have a form with some DIVs set to display:none;, any file fields that are in the hidden DIVs do not get submitted along with the rest of the data, whereas text fields are submitted. This inconsistency does not exist in Firefox 2 - it submits all of the available fields. Bad Safari, bad!
Just a quick reminder for myself: if you're doing a form that is uploading files, remember to add :multipart => true to the form tag, e.g.:
[source:ruby]
< % form_for(:product, :url => products_path(@product), :html => {:multipart => true, :method => :put }) do |f| %>