I think amyl alcohol, isobutanol and propanol are the most common fusels formed during fermentation. These tend to give hot, solventy, or harsh flavors. In clean beers like lagers they come off a bit fruity to me as well.
Some lager strains are very tolerant of ale-like temps (34/70 for example), but others aren't as forgiving. I tried running S-189 in the mid-50's with an early ramp to 62F, and it had quite a bit if fusel character. At lower temps, it makes a very clean lager.