A few facts on the congressional budget resolution (from Allen Shick's classic The Federal Budget: Politics, Policy and Process):

• For about the first 200 years of this country, there was no congressional Budget Resolution (BR) and no discretionary cap.
• The budget resolution was originally conceived of as a way to reduce deficits. When it didn't work that well, discretionary caps were added to make it stronger.
• The discretionary spending has decreased from nearly 1/2 the budget in 1975 (the year of the first budget resolution) to less than 1/3rd now.
• In 1975, domestic discretionary outlays were 4.4 percent of GDP. The Congressional budget plan for FY08 has it at 3.6 percent. That difference (by my back of the envelope calculation) is equal to about $100 billion in today's dollars.

For more on why the discretionary budget cap (or the congressional budget resolution?) may not be the best idea, see this post.