These examples are not comparable to what the OP was saying, e.g AOL/Time-Warner, Compaq/HP are mergers of giants with lot of employees.
BoA/Merrill Lynch
Shell/Royal Dutch
Sanofi/Avantis
Glaxo/SmithKline
P&G/Gillette
Roche/Genetech
Exxon/Mobil
Conoco/Philips
Disney/Fox
AT&T has had so many successful mergers that the government has basically had to split them up every time because it made them into a monopoly.
Should I go on?
EDIT: PS - DoubelClick in 2007 was considered "BIG". It had 1200 employees and was bought for $3.1B. Which was A LOT at the time.
These examples are not comparable to what the OP was saying, e.g AOL/Time-Warner, Compaq/HP are mergers of giants with lot of employees.