I have belonged to a sucky union that was useless. This was a place where the union had no power. Or at least didn’t care about junior members. This was a company where no one, from the most senior employee who wasn’t management on down, got their schedule more than one day in advance. The pay was barely above minimum wage. I frequently worked 12 hour days-- and lost count of how many times I had less than 5 hours turnaround between shifts.
In that case, the union did nothing but get in the way, take dues out of my pocket, and generally interfere with my work and the company’s.
I have worked, as a non-union member, in a unionized workplace. That was fairly amusing, since the union had way too much power. Let’s just say that staffing levels were extemely high. So high that frequently, union employees had nothing to do for 3 hours at a time, and so would stand around playing slugbug. Grown, middle-aged men, who were at work and not drunk at a BBQ, punching each other as hard as they could in the shoulder. Because there was no work for them to do, but they were paid for showing up. Sad.
I currently belong to a pretty damn good union, and as a student of organizational communications, I think there’s a fairly good give and take between management and employees. My shop steward may disagree, but that’s his prerogative 
Suffice it to say that at my current workplace, pay levels are acceptable, the workload is challenging and enjoyable without being soul-crushingly heavy, and the benefits are pretty good.
Unions have been in decline for some years. I think somewhere around 12% of the American workforce is unionized, most of that is in government, and most union employees are nearing retirement age… Which pretty much means that most unions are just gearing up for that one last contract to put their members out to pasture. Which ain’t right.
Now unions have done a lot to improve the workforce for everyone in North America. In fact, you could argue that the bubble effect of unions has made life too good for everyone, including non-union types, so that no one really remembers how bad working used to be. (60 hour workweeks the norm? No vacation days? No sick pay? <shudder> )
But take a look at the subtle factors of the workplace and people’s standard of living. Personal savings are at an all-time low, personal loans and credit card debt are at an all-time high, and most families have two people working. That’s a lot of work to effectively maintain the status quo.
I think the question is: Are we at a tipping point? Are we on the verge of an American recession, with fewer jobs in the U.S? Krugman in the New York Times likes to argue that the U.S. has become a nation of real estate agents and Wal-mart clerks, and while we aren’t there yet, we certainly are heading in that direction… and that ain’t good.
As long as the average guy can put food on his table, beer in his fridge, gas in his car and watch the latest DVD on his TV at home, he feels that he’s doing all right. But when he can’t? That’s when we’ll see a resurgence of useful unions. They’ll need to be relabelled, and they’ll need to concentrate on white-collar workers instead of blue-collar. But unions can be useful.