This is a very common concern before thinking for a siebel upgrade.  As per Anjneya "It does depend on the customization of the older application while doing upgrade.Higher the custom application higher the risk.

Siebel uses Denormalized Columns to improve the performance of query operation in view where data visibility is restricted using Siebel View modes like Organization, Position etc. Denormalized columns are generally created for columns most frequently used for query like Contact First Name, Last Name etc. 

High Interactivity and Standard Interactivity are Types of User interface.
High Interactivity is available for employee Applications supporting highly interactive enterprise users and requires internet explorer 5 or more.
Standard Interactivity is available for customer Application and behaves like traditional web applications, requiring frequent page refreshes.

Siebel Pricing: Aggregate Volume Discount article was much appreciated by readers. A reader has problem in enabling Tiered Volume Discount for an order having multiple order line items of same product . Lets look in to complete query and its resolution suggested by us.

It’s well known that a workflow requires an error control for a robust process design. The next diagram shows an overview of the proposed error control.

In this artice we will discuss on how to configure a VBC for invoke an EAI WF with a minumun amount of scripting. 
   An article by Siebel Expert Daniel Rodriguez 
This post show how to configure a VBC for invoke an EAI WF with a minumun amount of scripting in siebel.
Steps:
a) Create a VBC based on class “CSSFABCVRec”.