Rancilio's "home" espresso machine has quite a cult following.
Beginning life as a one off factory "gift" for Rancilio distributors, it became so popular that Rancilio started regular production of it. We're not sure it's worthy of the over the top accolades, but "pro like" construction, with a heavy steel frame, full size portafilter, 3 way valve, and brass boiler, it's far closer in build quality to "commercial," than most home machines in it's "mid" price range.
People love the Silvia's brass boiler (unlike the stainless tanks of most competitors) but it's small enough that any real advantage from the mass of the brass is dubious. The bigger "issue" is the same one most "home" machines have, with conventional "on/off" thermostats and small boilers. The heating elements cycle on and off in a fairly wide temperature range, so they get "hot" spots in the temperature cycling. Thus, adding a PID is a popular hack with owners of these.
A PID is a digital switch that will "flatten" the heat fluctuations by making the heating element cycle on and off in much tighter increments than a normal espresso machine thermostat. Whether adding a PID is "worth" it (meaning you can taste it in the cup) is like all things coffee, a matter of "taste."
The various "versions" over the years have been mostly cosmetic trim, but the latest addition of the replaceable stainless steel heating element (and boiler that fits it) in late 2013 is a major improvement. Otherwise, the upgrade to a swivling steam arm with V3 is the only real "version" change to care about. ALL Silvias are upgradable to these improvements, so any year can be made to "new" specs pretty easily (if not cheaply!)
The steel frames tend to have pockets that hold water and allow rust to form. Obviously that doesn't effect the espresso quality, but since the major selling point of the Silvia for a lot of people seems to be it's "commercial like" aesthetics, if the idea of a rusty frame bothers you, this is something to keep in mind. It happens to almost all Silivias eventually.