[kylekohlmorgen]

Fermcap is where its at.

Since I brew 5 gal batches into 5 gal buckets, I add a few drops after pitching in every beer (except sours - not sure if it would inhibit pellicle formation).

[bboy9000]

Losing beer due to blowoff never really crossed my mind.  Just by its appearance most of the blowoff seems to be yeast.  How much of the blowoff is actually beer?

For increased headspace I use a 6.5 G glass carboy with a blowoff tube and recently found an 8G plastic bucket at my LHBS:

http://www.apexbrewwares.com/Brewing-Equipment/Fermenters-Bottling-Buckets-and-accesories/8-gallon-Fermenting-Bucket.html

I haven't needed to worry about blowoff with the 8G bucket so far but I haven't fermented with any aggressive Belgian or weizen strains in it yet.