This can occur if there are a large number of files under a first level folder off the root of a drive. This is by design and is due to application compatibility. Add/Remove Programs uses Rundll32.exe to search under "Program Files" and also "Documents and Settings\<user profile>". However, some applications install directly to a folder on the root of the drive, and in this case would not be found by Add/Remove Programs. Because of this, Add/Remove Programs is designed to search first level folders located on the root of all local drives. If a first level folder has a very large number of files, this operation can take an extended period of time to complete.
This issue applies only to local drives or drives that appear as local, such as SAN drives. Mapped drives or other network drives are not searched by Add/Remove Programs.