- Safari: replaced by Chrome which feels snappier to me; also keeping each tab in its own process means this browser crashes/hangs far less than any others I've used
- MobileMe: replaced by iDisk with Dropbox and contact syncing using Google Contacts (which can be synced via a setting in the OS X address book). I also sync calendars between my phone and desktop using Google Sync.
- Time Machine: replaced with CrashPlan - backs up my data to the cloud and to a local hard drive, and lets me back up multiple drives; I find the UI much easier to deal with than Time Machine which tries too hard too look cool. I used to use JungleDisk but the S3 storage got to be expensive. CrashPlan
is pretty cheap.
- Date/Time menubar widget: iStat Menus has a super sweet, very customizable clock widget. I like being able to get a quick look at a calendar while I'm in other apps.
- Stickies: Replaced by Evernote so I always have my notes ready across all devices. Jehan Alvani suggests Yojimbo.
- TextEdit: Jehan suggests replacing it with TextWrangler or BBEdit.
- iCal: Replaced by a Fluid single-site browser running Google Calendar
- Mail: Replaced by Mailplane; same concept as my iCal replacement but Mailplane gives you some nice OS X integrations with Gmail as well as the ability to switch between gmail accounts. Mark Sim suggested Postbox.
- Spaces: Mark also suggests replacing this with Hyperspaces which looks really cool. I've never been able to get into using Spaces and this might be why.
- Terminal: Replaced by Iterm2. It has many nice features but being able to use apple-number keys to switch tabs is killer.
- iTunes: Partially replaced by Pandora. I hardly ever listen to songs in my collection anymore.
- iChat: I haven't tried it yet, but many people told me via Twitter that Adium is a very good replacement
- QuickTime: Chris Ensey suggests VLC as a replacement (probably because it handles more formats)
- Apple-Tab: Kyle Oba suggested Witch as a replacement; I'll be checking this out for sure.
- Keychain: I keep everything sensitive in 1Password which syncs pretty decently via Dropbox. Avdi Grimm and Ben Hamill both swear by LastPass which looks much more cloud-oriented, so if I didn't have so much data in 1Password already I would definitely try them out.
- Preview: Paul Capestany recommends Skim for reading PDFs and ebooks and taking notes.
- SizeUp: for moving windows around rapidly
- Alfred: super powerful way to do web searches, launch applications, and do simple calculations
UPDATE: follow some further discussion over at Hacker News