I have ran HIDs in my 640 Adventure for more than 80,000ks. I absolutely love them. I first tried a 35w set and they were great. I am now running a 55w set and they are better still. I prefer the colour the 4,500K bulbs over anything else. eg:- I had a set of 6,000K bulbs and to me they were just too white. Wouldn't mind mind trying a 75w unit in the high beam sometime in the future.
It certainly is possible to convert the standard head light on the Bergs to HID. I have just done the H4 halogen conversion to my '10 FE450, so it would be relatively easy to convert that to HID. Mounting the ballast unit will require a bit of thought and due to space constraints, it would probably be best to spend the extra $$s and get the latest 'slimline digital' ballasts. As much as I like the 55w units, I reckon the 35w (4,500K) would be more than enough for my needs. Trails, not high speed desert blasting.
I have recently purchased a set of these LED lights
http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWAX:IT
and while I haven't mounted them to my bike yet. I have hooked the up to a lead that I can run from my car's cigarette lighter. These are pretty damn good.
I have also spent a lot of time over at the Vision X Superstore (makers of the Solstice LED lights). Their Solstice Prime lights are very interesting.
http://visionxsuperstore.com/led.aspx They may be a bit pricey but would definitely be worth it for the serious night rider.
Clearwater Lights also make a high quality LED light - the Krista -
http://www.clearwaterlights.com/infopg_krista.html These are also dimmable.
Really wish I had the time and money to explore lighting these options better.