Regular Guiness has an ABV of ~4.2% or so, not far off what you see with typical domestic beeds like Bud (although higher than uber-lightweight beers like Mich Ultra, etc). Typical craft brews - nothing extreme, just run-of-the-mill pale ales and such - will generally run ~5% - 5.5%. IPAs, usually 6% - 7%. Get into "big beers" like Russian Imperial Stouts or Imperial IPAs and you're looking at 8%+.
All depends on the particular brewer, but Guiness is a beer that people tend to perceive as being more "hardcore" than it really is because it's got a ton of flavor from the heavily roasted malts they use. It's really not that far removed, ABV-wise, from typical domestic beers.
Still a great beer!