Yes, it is exactly what it sounds like: Christian bands joining the ever expanding genre of black metal. I was a little incredulous when I first heard about it, as it seems like something of an oxymoron. But then I guess black metal is more about musical style then lyrical content, so why the hell not? Maybe joining the ranks of the oh-so-deadly Mayhem and the ever-so-fashionable Cradle of Filth may not seem like the best way to win converts, but of course your run of the mill metaller probably isn't the target audience.

My interest piqued, I decided to listen to a sampling of the music.
All bands were found by way of www.blackcauldron.net, and all songs taken from the band's websites.

Crimson Moonlight
Sadly, nothing to write home about. The recording is horrible, especially for a band attempting to use so many instruments. The lyrics are a little cheesy, even by black metal standards. However, you can hear some talent through the muddy recording. Though as a band they don't do anything too inventive, technically they play fairly well.
www.crimsonmoonlight.com/cm/

Demoniciduth
If their was ever a garage rock sound to black metal, these guys have nailed it. There's no raw thrash like early 4 track black metal, but instead a very chugging rhythm to their style. Almost no production quality in the recording, and I kind of like it. The guitars lend themselves more to death metal and the drums sound like classic punk production. The vocals, however, are your basic gravel scream of black metal. The lyrical content is well, actually kind of funny. Here's a sample:

A satanic metal music fan turning on his stereo,
listening to stupid anti-christ bands singing against The Holy One

www.demoniciduth.cjb.net

Draco
Probably the best part about this band is the drummer. He can seriously throw down. The guitar is good, but trips up into some very strange tech licks. The vocals are so-so, with the black metal voice being fairly good, but the "clean" vocals are really lacking. The lyrics are kind of interesting, in that they tend to tell a tale from the Bible. Altogether, not that bad of a band. Very fast, with a heavy bend towards Power Metal.
www.angelfire.com/mi/dracohome/

Slechtvalk
My pick for "where it's at" in christian black metal. It's basically a one man band (Burzum, Judas Iscarot) and he manages to pull it off very well. Keyboard driven, thrash-tone guitars, and while the drumming and vocals aren't really that inventive, it's impressive for a one man project. It's fast, mean, and manages to stay fairly melodic. I can't tell you about the lyrical content because I couldn't find any on the website, and it's damn near impossible to understand black metal vocals. I did find it a little strange that there is no mention of Christianity anywhere on the site, and he lists influences such as Thyrfing and Immortal (who are definitely not Christian).
www.slechtvalk.com

Well, that's just a smattering of bands, but all together not that bad. My personal thoughts on the subject? More power to 'em. It has to be tough to play as a Christian black metal band, and I'm glad to see someone adding a new element to the genre.