e2d4d3c created the issue

Cyberduck 2.6 (2315)
note: exact app version is most likely unimportant to this bug.

MacOS internally uses the colon (:) as a hierarchic separator in file paths, which makes the internet-standard forward slash (/) available as a valid character in filenames and directory names. If Cyberduck is located in a pathname which contains a forward slash somewhere, Cyberduck will launch but no windows will open. The application will not be useable. Example location which causes problems:

/
Mac HD/
Applications/
Internet/
FTP / SFTP/ <--- problem point
Cyberduck 2.6/
Cyberduck.app

Workaround: Move the Cyberduck folder, or rename the folder(s) in between to remove any backslashes.

Note: this workaround will be inobvious to non-programmers, who are unlikely to guess the reason why Cyberduck isn't working. Since other FTP/SFTP clients launch and work fine in such locations (Fugu, Fetch, LiFTP), the inexperienced user is more likely to decide that Cyberduck doesn't like their system, and use an alternative app.

Extended workaround: Include a ReadMe file, and mention this problem, so inexperienced users will know what to look for, and how to fix it.

System configuration:
Mac OS X 10.4.6
PowerMac G4 (AGP - Sawtooth)
Gigadesigns upgrade card: G4 7455 at 1.1 GHz
2 GB RAM
dynamic DSL at 320/1200 kbs