There are plenty of similarities - one party controls Congress and the White House. There is mass dissatisfaction with the ruling party. That party is seen as arrogant and out of touch. There is a groundswell that is looking for change; the majority party suffers retirements and scandal.
However, the difference is in the underlying structure of the opposition.
In 1994, the Republicans had not controlled Congress in almost fifty years. They had been out of power a very long time, and in that time, had slowly learned that they needed to organize and work together to achieve a majority in the House and the Senate. To that end they had built an entire infrastructure to help create that outcome. They had established magazines, going as far back as the 1950s. They had created a number of grassroots organizations ranging from the Young Americans for Freedom to Focus on the Family to the Conservative Caucus. They built a system of think tanks to set their agenda, create ideological homogeneity, and begin to train future legislators, with the Heritage Foundation, the American Enterprise Institute, and others. There was a dedicated fundraising group that had perfected the art of direct mail, and could rely on big money business donors as well. For years, they had been working on getting people elected to lower offices, from the school board to the state house to have viable candidates for national offices. In the House itself, they had an active and aggressive leadership led by Newt Gingrich. He also set up GOPAC to train "people to speak like Newt."
These people had longed for the majority since the 1950s, and they had worked hard to create an organization that would both give it to them, and allow them to keep it. 1994 was the opportunity they had been waiting for, and the Democrats were not prepared. The Republicans took advantage of the weak and disorganized Democrats to take Congress, and with the help of their infrastructure, have not given it back.
If the Democrats are fortunate enough to take Congress this fall, it will be in spite of their organization, not because of it. And because they do not have an infrastructure to fall back on, it will be that much harder to retain the House and/ or the Senate in future elections. The Democrats will win because events favor them, not because of their own plans. While Dr. Dean is doing great work, and the 50 State Strategy is finally becoming conventional wisdom, there is a very long way to go to bring the Democratic Party as a whole to a level of organization comparable to that of the Republicans (and it will never be as good, thank god, because we like a diversity of opinions). That structure is not yet in place. A winning majority will be unstable for the following electoral cycle because the Democrats will win by throwing the bums out, but without a coherent message, they themselves will be thrown out by people who do have one.
Unlike 1994 which was the product of long years of work, preparation, and organization, 2006 would be an epic fluke.