The basic answer is it depends, it depand on what application you are running, what Operating system and patch level you are running. but on the whole most modern MS based OSes can be hot cloned,
applications that will not hot clone well are SQL servers, Exchange servers and Domain Controllers, in fact the last one the recommendation is to just create a new DC and move FSMO roles if necesary.
With the latest versions of Converter you can utiise MS VSS technology to trickle convert your machine, this will result is a slower but more stable and less intrusive migration. (think Storage vmotion or vmotion where the transfere is done and then finally synced before change over).
I would advise you to read the converter documentation
Also I am moving this post to the dedicated Converter subsection of the forum,