I'm not opposed to house rules, just so long as they're properly tried and tested, and are not just there for the hell of it. I don't particularly use house rules, since it's hard to get them right.
Campaign rules, on the other hand, are completely different. Since they're usually going to be one-offs it doesn't particularly matter if there's minor imbalances, and I'm usually observant enough to spot anything drastic. I've got campaigns written up in advance, ranging from the one-day to the truly epic confrontations, each with some complex additional rules.
The best part about campaign rules is, though, that as they aren't for fixing the game but making it more enjoyable, you have a great deal more freedom in what you can do before it's all too much.