I've just moved one of my domains to the free version of google apps and enabled DKIM.
Enabling DKIM means adding a TXT record which is "quite long" (235 characters). The display box in the DNS control panel, doesn't "word wrap" which makes the page a bit mangled...
I appreciate its a free service :-)
I have seen worse. At one point I came across a recursive DNS resolver, which was incapable of handling TXT records longer than 127 characters. I am wondering what will happen if domain key records grow beyond the 255 byte limit on the text strings. I have yet to see a service, which supports multiple text strings in one TXT record.