Yup, we live in Germany and our son has been riding in the chariot since he outgrew the "baby bivy" that Chariot sells for the really little ones, which was when he was 6 weeks old or so. He is now 4 months and we use the "infant sling" by chariot (and yes, Chariot must make a killing with their accessoires...). As we don't own a car, he is in there quite regularly, up to 4 times a day (going grocery shopping, picking up the big sister from kindergarten), maximum distance for a one-direction ride on a normal day is 2 miles, ie he travels a maximum of 8 miles on a weekday, I'd say. Longest stretch we biked with him is probably around ten miles in one go, all smooth (well, as smooth as the bike paths get...).
We feel very comfortable with this, although even in Germany, people are concerned about the horrible impact of a bike trailer on the spines of the little ones. I think that it is all a matter of using common sense: I don't take him mountain biking, I try to steer clear of potholes, I go much slower than usual on the road and on the bikes paths, I actually take different routes in order to avoid cobblestones or crappy surfaces, I don't keep him in there for hours or hundreds of miles. But if it's smooth tarmac, I don't see why it should hurt the kid to have him in the trailer for an amount of time that you would also have the child in a stroller. Just my five cents...
Interesting to read on their homepage that chariot is not recommending biking with the "infant sling". The German homepage states that "due to divergent standards in North America we recommend to use the baby sling over there only for taking walks". It quite clearly reads like "We are afraid to get our behinds litigated away in the US, that's why we essentially state that you should not actually use the bike trailer as a bike trailer. Feel free to do whatever you feel is right if your live somewhere else."
If anybody is interested, here -
http://www.veloplus.ch/pdf/news/kinderanhaenger2007s.pdf - is a report from a Swiss bike magazine (sorry, it's in German only, but maybe google translate can convey the gist of it...) that equipped some kids with some electronic device measuring the g-forces at work. In a first chart, they show what g forces a 2 year old generates by running (up to 3.5) and by jumping down a stair (19cm in height) (up to 8g). In the second set of charts they put the same kids in different trailers, went on a 3minute bike ride at speeds between 15 and 20 km/h that included different surfaces (including cobblestones) and a 17cm curb stone and measured the g-forces with the same instruments. Result: Maximum of 5.5 g in an unsuspended trailer (Croozer).
Yes, the test set-up has flaws and is imprecise and whatever. 3 month old babys are also quite different from 24 month old kids. Yes. But still - what I take from this test is that unless you go down a curbstone, a single trail or a pot hole, you hardly generate g force beyond what kids are generally built to endure.
Semi related: If you want some perspective on different modes of kid's transport :
Babies Celebrated: Beatrice Fontanel: 9780810940123: Amazon.com: Books
And also only semi-related: I am waiting for the day that some manufacturer comes up with a way to really click a car seat into the trailer, so that you don't have to mcguyver some solution like you did. AfaIk, NordicCab is the only manufacturer that does that for a baby car seat, but for us that would be interesting for bigger car seats, too.
Keep on riding, looking forward to my 2 months of parental leave coming up next January...
BTW: We have the very same toy monster...