I have switched my main computer from a Mac Book Pro to a laptop running Ubuntu Gutsy Gibbon. I have been pretty pleased with this switch.
Google Bookmark Sync - As soon as I installed this extension, all of my bookmarks, passwords, cookies, and history appear in the new installation of Firefox.
Web based applications - I have been used web based applications for things that are normally desktop applications. For example, I use the web interface of Google Mail and Calendar for mail and calendar. I use Remember the Milk for to do list. And Google Docs for word processing and spreadsheets.
A good password manager - On Mac OS X, 1Passwd is great. It integrates with all browsers, and it uses the built-in keychain. In addition, it will create secure passwords, all from the browser window.
A good MovableType blogging client - ecto is a great application for posting blog entries. I haven't been impressed with the applications listed in the Ubuntu add/remove application.
I am seriously considering the same. Currently I work off of three computers: my desktop, my work/research desktop, and my notebook. My work desktop has always run a Linux distro but I recently converted it to Ubuntu Gutsy. I just installed Gutsy (Tribe 5) on my MacBook and am currently updating it to (Beta). Honestly the thing keeping me on Mac on my home desktop is the fact that I have an iPhone and want to sync mail/calendar/music/contacts.
I used to fiddle with Linux installs a lot, but since switching to Mac 2 years ago I've never been happier. No more fuss with video drivers, broken hibernation, and problem with missing drivers. Maybe Ubuntu has fixed all this since I made the switch?
Welcome to Ubuntu. I'm using it exclusively since Dec. 2006 and am very happy with it.
I'm using Relevation, it integrates very nice with Gnome (including a panel applet).