Overall, a good beginning overview of Light 'Mechs.
One point where I will differ with Eric is that I do not believe that Light 'Mechs are the best means of dealing with opposing Light 'Mechs. Since Light 'Mechs in both forces are forced to keep their speed up to survive, you're looking at fairly high hit modifiers even with things like pulse lasers, and unless initiative order goes in your favor, an enemy Light 'Mech typically has the mobility to slip outside the range where such weapons are effective. Finally, it's rare that a single Light 'Mech has sufficient firepower to drop another Light 'Mech on a single turn when the opportunity presents itself.
I prefer a two-fold method for dealing with Light 'Mechs.
1. - Put Medium Pulse Lasers on all your fire support 'Mechs. Even with a secondary target modifier, it's a net -1 to hit, and just a pair of them can be a serious threat to a Light 'Mech when they connect.
2. - Utilize fast Medium 'Mechs to cover targets that Light 'Mechs want to strike. When a Light 'Mech makes an attack run, bring your Medium 'Mech in on it as close as you can. A single round of fire from a Medium 'Mech at short range, particularly if optimized for Light hunting like a PXH-3PL, will easily cripple it. Then, kick the sorry bastard for good measure. Only the most heavily armored Light 'Mech won't take internals from a Medium 'Mech's kick, and if you crit the leg or pop it off, the Light 'Mech is effectively dead.
Some of those slower light mechs are also very useful.
Maybe back in 3025, if you are strapped for cash/BV/tonnage/what-have-you. The Panther didn't stack up too bad in 3025, but on the post-3050 battlefield, a slow Light 'Mech is a death-trap. Panthers, Eagles, Hollanders & Falcon Hawks are just too easy to kill and removing their big guns from the battlefield is just too important to pass up. Pushing them further back in your formation protects them somewhat, but it also costs them accuracy, resulting in getting even less value from the unit overall. Outside of a militia desperate for
any 'Mech they can get, there's very little place on the modern battlefield for a Light 'Mech slower than 6/9, and even Lights that fast have to be very well put together to be effective. 7/11 or faster is pretty much a requirement to survive.
I'll be honest. I hate most Inner Sphere Light 'Mechs. They really are hard to justify after the Succession Wars, after the new Star League-recovered weapons begin to roll in. You can't dive headlong into battle with Light 'Mechs and hope for the best--they're not the sharpest tool in the box.
I've complained a lot about the "3025" school of Assault 'Mech construction, but there's a "3025" school of Light 'Mech construction as well. It's equally obsolete on the modern battlefield, yet you still see a lot of new designs relying on it. 3025 was an era when a +3 movement mod made you almost invulnerable, and a lance of Locusts could make an attack run on a lance of undamaged Heavy 'Mechs and live to tell of it. Those days are gone, yet we still see a number of 'Light 'Mech designs being made that assume that sort of strategy or a Panther type "Pocket Medium" strategy can be successful.
There are, however, a wide range of very good Light 'Mech designs for a set-piece battle if you look for them, such as the Duan Gung, the Talon, the Anubis, Ebony, & Wolfhound. What all these 'Mechs have in common is both high speed and the ability to strike at long range. Units like this can strafe back and forth behind your main combat line, remaining essentially immune to return fire, while still contributing to the battle, but in position to attack any flankers which might get around the line.
Outside of those types of units, however, most Light 'Mechs on the modern battlefield are and should be focused more upon utilitary roles of infantry & vehicle suppression, recon, artillery spotting, dispatching crippled enemy units, and backstabbing. A flamer on a Heavy 'Mech will allow that 'Mech to deal with any infantry it encounters. a flamer on a fast Light 'Mech will allow it to deal with any infanty the entire company encounters. TAG on a Heavy 'Mech allows it to call down artillery to support it's advance. TAG on a fast Light 'Mech allows you to call down artillery
anywhere on the battlefield. Getting there with the tool you need is what the modern Light 'Mech is about.