In regards to this thread, there are a couple issues that I want all of you to be aware of:

Age Restrictions

When you put money into a 401k, you cannot pull the money out until you are 59 and a half. Granted, you can take a LOAN against this money, but I wouldn't recommend it.

Taxes

The money that you put into a 401k is taken out on a pre-tax basis from your paycheck. This money is then put into the account to grow on a tax-deferred basis (meaning that you won't have to pay taxes on the dividends and growth until you take it out). When you pull the money out, it will be taxed at your income tax level. It is also important to note that during retirement, your tax bracket isn't always lower than it is when you are moving to the point of retirement. Most people no longer have their mortgage deduction, they no longer have kids around (and thus the deduction) and in most cases, they want to lead a similar lifestyle to what they used to, thus their tax bracket can stay the same or even INCREASE.

Maximum contributions per year
It is also important to note that you can only put a total of $4,000 in either a Roth IRA or a Traditional IRA per year.

Balance between something like a Roth and a 401k/Traditional IRA

The important thing to note is that a Roth IRA is absolutely superior to a Traditional IRA. In the case of a Roth IRA, you put in post tax money and it grows for you with no taxes. When you pull it out, you WILL NOT pay taxes on it. In the case of a Traditional IRA / 401k, you are going to pay the income tax on all that growth. It is a simple question of whether you want to pay the tax on the money NOW, while it is small or later, when it is big. What muddies the water a bit is the match from employers. That match can offset the downside of paying a huge tax later. So, I typically recommend that people put as much into their 401k to get the maximum match and then everything after that, they should put into a tax-free savings vehicle like a Roth. But, they can only put up to $4,000 into said Roth each year, so if they want to go over that, we need to explore other vehicles.

Rollovers
The reason that most people roll their money in a 401k over to an IRA is very simple: control. When that money is in the 401k, the company is in control of it. They have posession of it and it has to be in their investment choices. Look at what happened to the people at Enron with their 401ks. The company took them all down with the ship. When you roll that money into an IRA, YOU are now in control of the money and you get to choose where it goes (among the thousands of investment choices on the market).

Whoo, that's enough for me right now. If anyone has any specific questions, let me know.