Let's make this very clear and simple:
Bush's proposed plan will have no effect on the Social Security trust fund imbalance.
If it receives $100 less from you today, it will pay you $100 less (adjusted for interest) in the future.
The plan would have many other effects, but fixing the trust-fund deficit is not one of them. Potential higher returns from equity investments will not go to the trust fund.
Don't let them claim what's patently false. Use it!
Krugman's NYT OpEd today explains this somewhat less succintly, but still clearly and cogently.
http://www.nytimes.com/2005/02/04/opinion/4krugman.html