Can you use the new energy conserving light bulbs in ceiling fixtures with plastic/glass covers over them?

Are there any hazards in using the new energy saving lightbulbs (other than breakage if they drop & release mercury)? Is it safe to use them in a ceiling fixture with a standard plastic enclosure. How about in a combination ceiling fan/light fixture with a glass cover? Each fixture currently takes a maxium of one 60 watt incandescent bulb. If I put new energy saving bulbs in them, can I use ones with a higher light output?