I have one and it's excellent; my wife and I often use it in place of the 50/1.5 because it's smaller, lighter and takes 39mm filters instead of 52mm. It's beautifully finished and very easy to use, like an old Leica lens. It's true that it's not brilliant at f/2.5 but even f/2.8 transforms it to a superb lens and at f/5.6 there's not much need for anything else.
Put it this way: it'll be going with us to Portugal in a few days, along with my 35/1.4 pre-aspheric Summilux and new 75/2 Summicron and Frances's 28/1.9 Ultron and 90/3.5 Apo-Lanthar. As Frances says, "I was never much for standard lenses until I got that, and now, well, it's my standard lens..."