I just love my Hassy, which is great in the studio. For shooting fast on the move, it's less than ideal though...
To tell the age of any Hassy, just look at the serial number. There's two alphabets in front of the numbers, and the code is as follows:
VHPICTURES
1234567890
So if you see serial number ER26384974 (or something like that), the body was made in 98 (i.e 1998).
For Hassy, you can fit virtually any lens on the body, which is why I like the system so much. Buy the older lenses to start off the system, and you can upgrade later. In fact, some of the old lenses have similar optics as the new ones, except the latter has better flocking inside and better shutter mechanisms. So some of the older lenses (eg. the 150mm Sonnar) represents very good value.
The lenses are listed here in terms of age:
T (usually chrome)
T* (chrome or black)
CF (black with black rubber rings)
CFi (black with grey ribbed rubber rings and electrical connections)
The T* series is quite a good buy, because of the robust body and the T* coating which is better than the earlier generation. Just make sure that the shutter works accurately, especially at the slower shutter speed, and that there's no oil stains on the shutter and aperture blade.
XMV is the marking on the flash post (to which you attach the flash sync cord). You can set the selector for either electronic flash or flash bulbs or magnesium powder, which takes a longer delay to ignite.
With the popularity of digital cameras, Hassies have fallen in prices and can be had for a good price. I'd go for them over Bronicas and Mamiyas (although these are very good brands too) because I like the mechanical feeling of Hassies. Do you know you can visit the factory with the serial number of your Hassy, and they can dig the records and you can shake hands with the technician who assembled your camera by hand?
Sorry for the rambling from a Hassy nut.... ;p