1)Unable to understand custom object, then we have to map   
that object to standard object.
2)To handle the runtime objects.
3)Using Regular Expressions.

1. Main problem is with Synchronisation.
2. Page navigations while doing like parameterisation.QT 
will captures the link.We should take care thar at the end 
of scenorio initial link has to b connected.
3. To handle runtime objects & regular Expressions....
Pls let me know more if it is wrong.

While testing Web-based application,people might face 
object recognition problem. At this situation, one can use 
Smart Identifier. Once it is used in the script and run it, 
in the result window, they can find out which are the 
properties to uniquely identify specified record. after 
that without using smart idenfier one can execute script.

One of the challenges user face with QTP web based 
applicatons is 'Working with Dynamic Objects'. If we have 
dynamic objects on screen which can be part of a table or 
otherwise as well. Descriptive programming is the only way 
to work with these kind of objects in QTP.