Nets angling for Thursday prize: biggest fish still at large on tight night.(tv)(television networks)

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.

"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.

But as shows age, no one has an ultra-dominant player on the night anymore. And that leaves some webheads …