I'm a competitive long-distance runner with a pretty intense training schedule, and I firmly believe that my regular yoga practice (Bikram) has helped me stave off a few injuries and stay more loose, flexible and balanced. But when I developed this nagging soreness in my sacroiliac joint (between the lower back and the hip), I started investigating various ways to strengthen my core. While yoga helps boost strength and flexibility (both good things) Pilates tends to rule at strengthening the abs, especially the obliques. It's also great for strengthening and bringing more flexibility to the hips, back, and hamstrings. So I'm giving it a go, and will start taking a mat class at my local Y on a regular basis. I also plan to be more diligent at doing crunches on the stability ball, leg lifts for the inner/outer thigh, squats, lunges for the hips and butt, and more. If you're interested in Pilates, there are loads of places in and around the city to practice, most of them kind to first-timers. Feel free to comment on your favorite studio for other readers. Meanwhile, I'll keep you posted on my progress!
When you focus on stabilization in the asanas, you will gain more core strength with yoga. Many modern teachers focus so much on flow and "power" yoga, which is also wonderful, holding a pose will almost always get you in your core! (Pilates is fun too though!)