While answering a post in another thread, it recently came to my attention that there's another concern with the sensor bar: mirrors.
Any reflective surface will throw the sensor bar off if given a signal from the Wiimote. In some instances, you might get a duplicated command, while in others, it might just go squirly.
I do believe that they've compensated for this by limiting the signal to a certain range of frequencies, but there's still the possibility that a close reflective surface could do some harm.
It's just another thing to look into when setting up your Wii.
Furthermore, while on the topic of the sensor bar, I was looking into the whole sunlight issue.
In looking at a picture of the bar, you'll notice that the front is a dark semi-transparent plastic. The reason it's so dark is that the purplish-black color is actually a UV filter.
This, in addition to the IR LED's restriction of frequency, should take care of any problems sunlight would usually cause.