I'm new to dopus, testing it since a couple of days and it looks great.
The site says configuration is XML-based. Does this mean nothing is stored in the registry, and when I soon buy a second computer I can simply copy the dopus installation folder to it to transfer the app with all my settings and customizations?
And one more thing, where is the data about ftp accounts stored, is it encrypted, and if yes - how strong is the encryption?
I'm asking this because there are 'recovery' tools for almost any ftp app out there, which reveal the saved passwords in seconds. For some apps revealing the passwords is not possible, but copying some data files to another installation makes possible to copy the saved accounts from one installation to another. Then you can connect to ftp's, even though you don't know and can't reveal the password.
Use Settings -> Backup & Restore if you want to transfer your settings between machines. Then you don't have to worry about differences in where the two computers store their files and so on.
You still need to install Opus on the other machine since it has to register a couple of DLLs so you shouldn't just copy the Program Files directory over, either. Instead, install and then use Backup & Restore to import the configuration backup you made from your old computer.
FTP account settings are stored in XML config files on-disk. (Possibly in your roaming profile, depending on how Opus is configured and what type of account/network/domain you have.)
I don't know of any tools to reverse the encryption but it is not a strong encryption and it's not tied to your account in any way, so if someone else got your configuration files then they could connect to your FTP sites and may, with a bit of effort, be able to work out what the passwords are as well.
If you want to keep your passwords secure I would recommend not storing them in Opus. Instead keep the password fields blank and use a tool like KeePass. You can configure KeePass so that when you connect using Opus and get prompted for the password you can hit a hotkey which tells KeePass to automatically type the relevant password.
(KeePass itself can be secured with its own password, so you just have to remember one password to unlock all your others, and you can set it to stay unlocked for X minutes to make it easier when you're connecting several times in a row.)
It's also worth noting that Opus has a built-in "reveal passwords" option. This requires you to know the "master password" set inside of Opus but if you have not changed that from the default (e.g. because you didn't notice the option existed) then it's going to be very easy to reveal your passwords without having to break any encryption, provided the attacker has access to your config files.