A huelga is a strike by the general population. It is the favored form of public protest. They are common when times are tough, as they are now. Sometimes there are national strikes, other times they are local over some local issue, like failure of the government to honor its promise to pave the streets of a small town. Currently the strikes are over the miserable power situation in many locations and the very real financial crunch that a great many Dominicans find themselves in. Usually a strike lasts from one to 3 days. Between now and the election in 2004, you can anticipate an increasing number of strikes.
Some locations are more prone to strikes than others. Nagua and San Francisco de Macoris, for example, are always ready to strike. The barrios of Santo Domingo and Santiago are also fertile strike territory, as is Gaspar Hernandez east of Cabarete.
When there are strikes, buses between Santo Domingo and outlying areas may not run because the protestors are blocking the highways. Likewise, guaguas and publicos may not operate because they can't get where they want to go with out defying the blockade and risking a rock through the windshield.
There is no reason to panic if you are here during a strike. They are not targeting foreigners and they do not go on resort property. On the other hand, if there is a strike and the possibility that highways are blocked in some locations, you are well advised not to travel on the highways if it means going through the strike area as you are almost certain to have your vehicle damaged.
I've lived in the DR for 17 years and have seen a lot of strikes. Expect to see a lot more. They are not something to be afraid of, but you do need to take precautions to be sure you don't get mixed up on something that has nothing to do with you.