Most people want a CD for about 6 months to a year and they have money in the thousands to invest. Right now the best CD rates for that length of time top out at about 2.9% for a 1 year certificate of deposit. You have to look hard to find rates like that though, because if you just go down to your local bank, they will probably give you a rate more like 1.5%.
Historically, if you had more money to invest, a lot more money, you could get a higher rate. A jumbo CD is any certificate of deposit that is $100,000 or larger. If you were willing to give that much to a bank, they could get you a better rate than if you had say, just $5000 or so to invest.
Typically, the more you have to invest, and the longer you are willing to invest it, the higher rate you can get. Right now though, a jumbo certificate of deposit doesn't pay more than a regular sized CD. That's how bad things are right now. It doesn't matter how much you have, you can only get so much for your money. And that rate is extremely low.
The best CD rates are so low now that it is very discouraging for all the people with money to invest. Can you imagine giving up $100,000 for a year and only getting a couple thousand back in interest? It hardly seems worth it and leaves you with very few alternatives if you want to invest that money safely. This is why the recession is hitting retirees very hard who count on investment income to pay for part of their expenses.
There always was that saying that "time is money" but right now time is very little money. If you have enough money to qualify for a jumbo CD you are very fortunate that you have the money but unfortunate that you can't really make the money work for you.