There is one problem in dia that make diagrams looks a bit ugly. Then I draw 
two input-output blocks, they look like this:

  ----
 /   /
/   /
----
   |
  ---
 /  /
/  /
---

I either should connect them by slanted line, or move one block a bit so that 
connecting line became horizontal. I'd like to place those blocks one directly 
below other and connect them with vertical line. To do that it would be nice 
if connection will be sticked to the middle of object bottom line, not to the 
middle of object side.