Now that it is gone, I miss it a lot. I bought new MacBook Pro 13 to replace SP4. While yes MBP is easier to use than SP4 in a lap but I didn't realized earlier that SP4 allowed me to use it in more situations.
For example, I took it with me to office and took notes on it in meetings. I would never take a laptop to a social event, but didn't feel bad about bringing SP4 to a friend's place. While it is too heavy to use for extended period of reading, it was still great light reading, especially of small PDFs or magazines.
As for dev work, the screen area was usually on smaller side but completely usable. I used Netbeans and SublimeText for most of my work. In Netbeans, I would close most of extra panes to increase editor's area.
Just in case you are interested, I was using Lightroom to edit photos on it too. Again I had to close side-panes when viewing photos. But I really loved editing photos on it because of touchscreen/pen.
Lastly, I am keeping MacBook Pro 13 for now but I came very close to returning and getting SP4 again. :(