Regardless wether shieldwalls actually have a bonus to the covered area (i'd like to see that confirmed!), shields are huge in tactical play.
In the tournaments (small 8 vs 8 battles) we pair shielders with non-shielders so they have some protection from ranged. Also: shielders excel in facing multiple opponents. Because of the shield, you can easily tie down two or even three opponents. And because of the shield, you can maneuver into threatening positions that a manual blocker wouldn't consider (because he'd get shot or overwhelmed by melee).
In big, camp-style fights, the shielders can provide (mobile) coverage for archers. You can play personal protector for some good player (2h or polearm especially), tailing him and stepping forward to block swings he can't block. Or step in to block enemy fire.
With a shielder, you can breach enemy lines. Push through between their fighers and get in the middle and even behind them.
There are countless things we shielders can do that the none-shielders can't. A good shielder can be a valuable teamplayer without having to swing his weapon once. Deny areas, tie down multiple opponents, outflank groups and force them to face two directions. Often, it's smart not to risk dropping that shield, but even then it's still really worthwhile if you manage to disrupt their play, surround them, tie down and grab the attention of multiple opponents, etc. And we can chase down archers, if we have high enough athletics.
And i bet i forgot some other cool stuff shielders can do.
Edit: also, shields are not restricted to 1h users. All my characters have shields. I feel that shields get worthwhile with 1 or 2 shield skill. As a polearm or 2h user, that board shield allows me to cross areas that are unaccesible because of ranged fire. And if your willing to risk a few more points you can even go shield 4 or better on a 2h or polearm user, giving you some of the advantages the 1h shielders have. Only trick is to time that weaponswitch and hope they won't spam your shield. But even then you can retreat with shield up to teammates and then switch to weapon. Shields are great, even for the other classes.