When I first joined Christian Forums in 2007, the forums had just split into two sub-categories of SDA due to constant bickering between "progressives" and "traditionals." Usually, you won't hear either group identify themselves by that term though, so it gets tricky. There isn't a real difference that I could show you by drawing a line in the sand, but to put it generally it's a more liberal versus conservative divide.
I certainly can't speak for everyone, but generally in the progressive side of Adventism one will find less emphasis placed on the sanctuary and investigative judgment, as well as the importance and place of Ellen White's writings. You may (but not necessarily) find some progressive SDAs who claim the Sabbath is really of no real importance (I only say that because I personally knew a group of them in the past that were active on CF). Progressives will tend to support women's ordination, homosexuality in the church, and pro-choice more, though not always all of the above together. There are many other things that people get in minor disputes over, just as all Christian sects and denominations don't agree 100%, but the big differences you'll find in Adventism are what I mentioned above--1)Sanctuary and Investigative Judgment, 2) Ellen White, 3) Sabbath importance.
Hope this helps. And as a belated disclaimer, I'm certainly not trying to pigeon hole anyone.

I realize each individual is different from the last so it's impossible to label people straight across the board. Frankly, I hate the fact the SDAs are divided on here, thus I participate in both forums.
God bless,
Andrew