Ok, so now that I have manged to get it to work, some early testing results. Overall, the app feels quite polished. Here is my random mix of comments, bug reports, feature requests, in no particular order.

feature request: it would be nice to be able to have a visual clue in the app as to when the information was last refreshed. For instance by having a "last updated X minutes ago" or "last updated 12:35", or some such thing, at the top/bottom of the main application window.

GUI issue: I can see the status message of the services to the right. There are two issues with this: the first is a minor usability issue, that the i have to scroll to the right to see this, even though there seems to be enough space on the screen to show both the service name and the status in most cases. At first I had not even noticed the status messages are there. The second is that the status is sometimes truncated, for instance saying "DISK WARNING", but not the % of the disk that is used. Not sure what algorithm you use for the truncation, as some of the status messages from my custom nagios plugins are not truncated.

I am thinking that it would be useful to be able to see the whole status message, as 9% disk space is very different from 1%... but of course that won't work with the width of the screen. Maybe the entire status message could open when tapping an individual service, as a "child node" of the service?
Or alternatively a "details" window could somehow be opened (tap and hold on the service?), which might be able to also hold additional info such as the up/downtime, last check, etc .

Finally, I had some strange behavior when I first installed the widget... the whole hildon desktop seemed to be almost frozen, especially launcher icons which did not respond. I had to restart hildon-home several times (got the "is not responding" dialog), and rebooting did not fix the problem, so I removed the widget. However, I have now re-added the widget to my desktop and did not re-encounter the problem, so I don't know what's up.... If it does not happen again I will blame alien mind control and happily ignore the issue.