Currently, the message flow (i.e. connection from one web service activity to
another web service activity is peformed by 
Shift-Click on source element , 
then drag ( message flow line will be created as you drag) to the target web
service activity. 
Then drop on target.

The concern is that this is a useability problem as shift click is not a
desirable mode 
1) it is not intuitive, not many users know they need to do this without reading
 docs. Their expectation is to just drag and drop, not shift drag.

2) it is hidden. There is nothing to indicate which elements support connections
and which elements do not support connections.

3) it is confusing. Users are not sure whether they have to hold the shift down
during the entire drag process and then release both click and shift
simultaneously or not. This is not clear and users are sometimes confused.

Recommended Fix:
Te UI should use simple select and drag mode. The challenge of course is that
select and drag is also used for relocating elements (i.e. moving an element
from one location to another).

The two can be reconciled by creating renderign visible "message flow connector
handles" next to the Web Service activities. 
The user can then see that these handles exist. 
User can grab handle by simple selection of handle. 
User can click and drag handle in order to create line
User can release over target and that will cause the line to be connected.

User will still be able to relocate/move an element by selecting any part of the
element (other than the message flow connection handle) and dragging. So there
is nothing new or different for moving elements, other than the user shoul not
select the newly visilble message connection handles unless they wish to create
a message connection.