I only discovered the Minolta 135 2.8 in the last couple of months. Bought one of Ebay for $300 and finally had the chance to try it this weekend. The first thing you will notice is that this lens is super short and lightweight for a telephoto; it's about the same size as the FE 55 1.8 which makes for excellent pairing with the A7 (see attached thumbnail). Second the lens is super sharp even wide open, not as sharp as the Canon 135L but still plenty sharp; where it beats the Canon is in colors, it produces beautiful saturation and contrast. Also the Minolta has a very snappy and relatively quiet autofocus though not as impressive as the Canon version.
The lens' one con is its near lack of control for chromatic aberration. That said, I'm not sure if its because of improvements in LR5 or the uniform nature of the len's CA, but it is remarkably easily to completely remove in LR.
I love using teles for discreet street shooting but I'm often hampered by the weight and size, the Minolta solves this problem for me; and it's of course a wonderful portrait lens to boot.
Hartford 2 20140531 by Icon Foto, on Flickr
Hartford 3 20140531 by Icon Foto, on Flickr
Hartford 1 20140531-Edit by Icon Foto, on Flickr
Hartford 6 20140531-Edit by Icon Foto, on Flickr