I’m working mostly in Ubuntu now a days, and its been a joy since I discovered (read: desperately scoured the earth for) these fantastic applications that give me all the workflow magic I take for granted in OSX.
GNOME Do
A very fast and extensible launcher that does all the stuff I use Quicksilver for in OSX. If you’re not using a launcher, you are wasting time.
Gedit
Gedit is an understated program with unlimited potential. In that way, its the Preview of Ubuntu (even though its nothing like Preview). Actually, its the TextMate of Ubuntu if you turn on Snippets in the preferences.
Firebug
Not strictly Ubuntu, but I use it constantly. Even though I haven’t been building websites recently, I often use it to quickly reformat webpages on the fly so they work better in the size of window I want to view them in.
Sticky windows
This is enough to make me question my allegiance to OSX altogether. Sticky windows, in fact all the X window behavior is truly excellent. I can easily set up my desktop using every inch of available space and I don’t have to look for anything hidden behind some window because it’s all right there. In comparison, when I’m in OSX my desktop is a mess. What is with only allowing window resizing on one corner!? That’s just foolish.
Actually useful virtual desktops
Spaces in OSX is unusable, because in Macland you open a program once and all other instances of that program are just windows of that original program. Try using Gimp in Spaces, I dare you. In Ubuntu, each window is its own independent program, so virtual desktops can be completely separate from each other. This is the only way to go. I can have Gimp spread out over one desktop, Inkscape on another; terminal, gedit, and Firefox open on a third and I’ve got everything I ever need for design and development at my fingertips. Its ideal. Its clean. I love it.