What? Goblins can't be characters now? You goblin-racist. I bet you're one of those Kobold-lovers, aren't you? The answer to "how many goblins can an Xth level character take on?" should always be "depends on what level the goblins are".
Actually I'm a goblin lover, not too fond of kobolds. That's why goblin is always at the tip of my tongue.
And of course, it does depend on the level of the goblin, I was thinking of "1 hit dice" goblins, or "standard level 1 goblin skirmisher" depending on which terminology you prefer.
On second thought, orcs might be a better comparison, since they specifically gave orcs as an example of a creature that might be challenging at low levels, but maintains its threat at high levels.
And really, it's hard to give numbers any way you look at it. A first level wizard might be able to take out 5 orcs, while a first level fighter can only take out 1, but the fighter can take out another one in the second encounter, another one in the third encounter, another one in the fourth encounter, etc, while the wizard's kill rate drops to zero after the first encounter. At level 10, the wizard might be able to take on 20 orcs in one encounter, only to be tapped out after that, while a fighter can take out 5 in one encounter, and continue to take out 5 per encounter. Meanwhile the rogue might only be able to take out 1-2 orcs per encounter, even at high levels, but the one he takes out is usually the shaman, or the chief, or the two snipers on the hill.
This business of what you can kill, is not a good measure of the effectiveness of a character. I'd go so far as to say 4e taught us that lesson if any previous edition had not, with the Warlord, and the Wizard.