Love your Catrike but hate sharing it because everybody needs a different boom length? Catrike is answering your frustrations with the release of a chain tensioner this June.  It was initially revealed at this year's Catrike rally, but information and a photo was recently posted to the Catrike forums.  Here's the word from Catrike:

Yes, we have designed a new chain tensioner as Devious and others have seen at our last Rally. It works great and will retrofit on all Catrikes 2005 and newer (2005 and 2006 may need new boom clamp) and is being manufactured by TerraCycle for Catrike. It will be anoodized and have our Catrike logo lazer etched on it.

It will be great for multi-rider Catrikes [...] and especially useful for test rides at our dealers. It will be available in June.

Just a side note - don't ever call TerraCycle and try to order trikes.  Sometimes having two companies named "Terra" in speed dial is a bad thing.