If you use the binoculars to mark a target, then switch to another class, the target stays marked. Sadly, it was just a 1v1 so I couldn't switch back to scout and mark another target... Imagine the handiness of having the enemy CV constantly marked without having any worthless scouts on your team. :p (The commander attack order seems to fizz out if you get far enough away from something, so that clearly doesn't count.)
More like 30, I spot every tank I go past. Really helps the team. And it doesn't require sitting next to a barracks changing class every ten seconds.
With some teams, you could give them a spectator's view of the battlefield, complete with an all-revealing minimap, and they still wouldn't know what to do about the column of AFVs heading for your CV. =P Problem with spotting over the radio menu is that it lasts 5 seconds, and some servers aren't so good with the minimap. It makes up for it (somewhat) by letting you mark stuff every 2 seconds or so. That gives the rest of the team a brief glimpse of what you're seeing, IF they're paying attention. (They never are.) Attack orders and attack orders are great for fighting, but it's sometimes difficult to tell buildings from vehicles from infantry from turrets. The scout's binoculars can only mark one target at a time, but that target will stay marked until it dies or the scout marks another target, and it's just as informative as the radio menu spotting. Pretty handy for keeping track of the enemy CV, or some particularly persistent threat. I'd be amused if this bug can be used to mark an entire base (with the help of an armory, of course).