Think about it this way:
When many Guardsmen take wounds, you think to yourself "Crap, they're dead." If you make a few saves, you think "Cool, some of them lived, they can still shoot their special weapon next turn."
But when Marines take a few wounds, you think "Well, they'll make their saves, because it's 3+." Then when a few fail, you think, "Crap! I lost a few Marines to Lasrifle shots!"
Ok, maybe that little dialogue was kinda lame.
It's been said, man for man, Guardsmen are not good. A single troop of any army won't accomplish anything, though. One Marine, one Guardian, one Hormaguant, none of them will accomplish anything alone. So why should Guardsmen be expected to save the day all by themselves?
Here's why I belive Guardsmen are excellent. To me, Imperial Guardsmen are the most versatile, cost effective troops in the game. With all of the options they have available, they can be tooled up to do anything.
Or, my way of doing things, is to send them into battle with thier Flak and their Lasrifle, and every two out of ten get either a Flamer, a Grenade Launcher, or a Chainsword, or the occasional Meltagun, should the need arise. You spend fewer points and get more men. Fancy doctrines and 25-point Lascannons may look like fun, but I'd take four Guardsmen instead, any day.
Wow, I'm turning every post I make into "Liek's Imperial Guard Tactics." Oh well.