Hello, I have been looking at both commercial and open source hosting control panels, mostly through online demos. But I've also installed ISPConfig and i-MSCP myself to evaluate them more in depth. I thought you might like to hear the initial thoughts of a new user and hopefully you might be able to answer some questions I have.
First, let me say that I thought ISPConfig was decent but that the end-user interface was entirely too technical. I do not think the average web hosting customer would know how to use it. So my search continues.
Now for my thoughts on i-MSCP.
Install:
The installation went surprisingly smoothly on a fresh minimalist image of Debian Squeeze. The only problem was a CPAN module was needed to run the install script, and I also had to install CPAN.
It would be nice to have more distro options, obviously, like RedHat/CentOS.
Can the configuration options that were entered during the setup process be changed at all after installation is complete? For example, I declined HTTPS support, but would like to add it. On another note, I would like to have the option to select a discrete port for SSL, so that I do not have to use up a dedicated IP address just for the control panel. This is important considering the shortage of IP addresses and slow adoption of IPv6.
Adding users
Apparently end-users can only be added by resellers, not directly by the administrator? Is that correct? It would be nice to be able to add them directly, in case one doesn't want to have resellers at all; however, if this was an architectural design decision for the software, I would like the overall concept be explained somewhere.
Exception on login screen
Entering a wrong username/password results in a "An exception have been thrown" message and numerous emails sent to the administrator email account. Is this by design? I do not want to be notified by email every time someone enters a wrong username/password. Also, the error message should be more helpful, e.g. "wrong username or password", not "an exception have been thrown".
User interface
I have found the overall user interface for admins/resellers/end-users to be eye appealing and easy enough to navigate. The layout is certainly simpler and better organized than even commercial control panels. There is room for improvement, however.
First example: clicking an option (e.g., users) and having to use a different navigation menu to add a user is not ideal. The add user button should be on the same page as the user list.
Second example: clicking the "OK" button next to a user's account disables the account. This is not intuitive. I also do not understand the "Reload" text that appears in place of the "OK" after it is clicked. Clicking it doesn't reload the page.
Domain alias feature
The Domain Alias feature is confusing, as it is really two features in one.
Domain alias to me means a domain name that either redirects to the customer's other domain or is added to the ServerAlias list for another of the customer's domains. When choosing the alias/redirect option there should be no prompt for a mount point.
If one chooses a separate mount point and not to redirect the domain, this really should be called an add-on domain.
Web hosts are going to want to be able to set different quotas for the "domain alias" and the "add-on domain" concepts as I just described them.
What is with the "awaiting approval" when an end-user adds a domain alias? If they are under their quota for domain aliases, why do they have to wait for approval each time? Is there some kind of notification system to alert the reseller of the awaiting approval?
Summary
I hope I wasn't too critical. If I did not like the software I would not be spending time here giving you feedback and asking questions. 
How close is this software to being ready for production use? Is there still a lot of work to do or is it more of a matter of some minor tweaks here and there? How quickly is development progressing? I certainly would consider contributing if it is needed. I am primarily a Perl programmer but can do PHP as well, and am also familiar with most of the daemon config files (apache, mysql, etc).
Thank you to the developers for your work on the project, and to anyone who gives me feedback on my feedback.
- maybe with the new setup it's also possible to rerun the setup (ir update) to change the settings... but I cannot tell this for sure.