They do get very hot.
We recently put in under-cabinet lighting in our kitchen, and I did tons of research trying to find the best lighting, and I found many people talking about how scary-hot their halogens were, and one person who had them inside her cabinets had them start actually on fire. We have some halogen recessed lighting over our breakfast bar, and they do get quite warm.
We got the fluorescents for under the cabs, but I am not impressed with the sickly glow of them. I cannot have a lot of fluorescent lighting, as it gives me horrendous headaches after a while. And my contact lenses absolutely HATE fluorescent lighting. My eyes look like their bleeding.
I am waiting for the LEDs to be perfected. They give off such a pure, bright light—when they work properly.
Until then, I am hoarding the incandescents. Up yours, Green Police.
The key to getting good results from fluorescent undercabinet lighting is to use quality, high CRI (Color Rendering Index) lamps. I prefer warm white (color temp 3000K or less) and you’re looking for a CRI of 85 or higher.
In Home Depots around here, there are GE T5s in green packaging over near the undercounter lighting fixtures that meet the need. The lamps in the replacement lamp aisle aren’t nearly as good.
If you are using T8s, you now know what you’re looking for, I’m not as familiar with exactly where to get “the good stuff” for those.