Can't say I know much about BNI (only heard of it here) but tag lines, yeah I like 'em depending...
For customers (and occasionally for myself) I will develop a tag line. I'll never forget the tag line I came up with for the enterprise software product I co-founded:
"Xfactory, the world will never be the same"
But I thought you might enjoy my dissecting of this tagline.
First, the product was in a space that had very difficult problems to be addressed, carried high impact on the companies that used it (good or bad), was overly expensive, and was swathed in a fog of confusion.
Xfactory was a radical solution, one that addressed these issues in a whole new way (in fact, it caused a ripple affect that restructured the whole market). So we came out with it HARD, bold and in your face - throwing down the gauntlet, so to speak.
It was the right play for this situation.
Another tag line I came up with was for a (now-defunct) mobile instant messaging company. They had a product that allowed a person on a cellphone to talk and listen to IM (such as Yahoo IM, AIM, and Windows Messenger). The phone user had IM messages "spoken" to them (speech synthesis) and the simple spoke their messages in return. I came up with the product name, Talk2Chat then the tag line.
"If you can talk, you can Talk2Chat"
Why? Because this market was general consumers that wanted cool stuff they could pick up and use - not have to think about and learn. The attention time they would pay attention to an ad was measured in seconds. The tag line had to instantly strike an interest, first read, first reaction.
Finally, for a more results based tag line I had this:
"DANGEROUS DREAMS AUTHOR GETS RESULTS WITH INNOVATIVE GUERRILLA MARKETING CAMPAIGN"
This was a tag line for a press release for my scifi book. It is filled with power words and "hot" words. It has a very specific message, and it slaps it home with assurance and confidence.
Maybe some of these examples will help you spur your imagination in the pursuit of new tag lines!