Since Tweetie was purchased from atebits you can definitely tell that priorities have shifted to align more with the focus of Twitter, Inc. Expected but unfortunately features that we have all come to love have been removed over time. This has been reflected in the Mac app as well as the iPhone app. ( Fred Oliveira sums it up well in his post Dear Twitter. )
Dropbox continues to impress me. It allows you to sync your files online and across your computers. It is for Windows, Mac and Linux. Not to mention they have an excellent iPhone app. ( And also iPad, Blackberry and Android apps. ) Sync is done automatically and without you having to think about it. It just works.