In this week’s Weekly Variety, I look at the broadcast networks’ changing competitive outlook on Thursday nights.

Thursday, of course, is the most important night of the week for advertisers — and as a result, is also a night that the networks treat with extra care. NBC dominated in the 1990s with “Must See TV,” but in more recent times, the success story has been spread around a little more evenly.

Even Fox is now finally in the hunt, now that its “Bones” and “Fringe” combo has helped the net flip the lights on.

An excerpt:

Thursdays just got a little more interesting.

Fox is on the rise with its dramas. CBS is experimenting with a “Mentalist”/”CSI” timeslot flip. NBC is itching to bring back drama at 10 p.m. And ABC is facing some likely changes on the night as well.

Traditionally the most important night of the week — the one advertisers most covet — the balance of Thursday power is shifting this season.

And that could make for some tough debate and interesting strategic decisions this spring, as the nets head toward their May upfront presentations.

For the first time in at least 20 years, all four networks have a solid performer on Thursday. Add in cable (where USA is also humming along) and at the very least, the news is good for the industry: People are watching a lot of TV on the night.

“As much as we all love crushing each other into the ground, when you’re thinking about the health of the business, it’s not a bad thing for everyone to have something to show,” a network exec says.

“It’s a good night for all of us to be healthy, and there’s no better health barometer than Thursday night,” he adds.

But as shows age, no one has an ultra-dominant player on the night anymore. And that leaves some webheads concerned, as the playing field evens out and the night’s pecking order is far from guaranteed.

Read the rest here. Or go get a Weekly Variety subscription already!

Below: A promo from NBC’s “Must-See TV” Thursday night heyday.