Abuses against people on the lower socio-economic level are common in today's society. Due to the many advances made by minorities and the expanded opportunities available for many people, the misconception that Habieas Corpus is an outdated recourse is common. However, there have been many recent situations that show otherwise.
Yes, it still applies today because the law was written to help people who were unlawfully imprisoned. Those who are imprisoned but can prove their innocence should have the ability to get out of jail. Thankfully, many people are now exonerated after false imprisonment due to DNA testings and other modern sciences.
Habeas Corpus is absolutely still applicable today. Usually writs of habeas corpus are used to review the legality of a party's arrest, detainment or imprisonment. There should still be a mechanism to ensure that a seizure of a person is lawful. Unlawfully detaining someone without cause should not stand. If someone is being arrested, there should be cause and he or she is entitled to know it.
There are certain buzzwords that the government uses to remove the rights of its citizens, and terrorist is one of those words. In almost all everyday life, Habeas Corpus still applies. However, the government very obviously has legal loopholes if they want to use them. This is exactly what the PATRIOT ACT is all about. It's no surprise that it's been used more in non-terrorism cases than in actual terrorism cases.