Actually, the Iron Banner bond increases Iron Banner reputation gains by 10% (As do the emblem and shader [they stack up to 30%!]).
Source: [url=http://www.bungie.net/en/event/ironbanner]here[/url] under 'Rank1'.
Apart from that and the Faction bonds, they are just cosmetic.
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Wish I knew that before I got to rank 4...
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Ya, it definitely shaved a lot of time off getting to Rank 5. They should've put it in the game instead of on the website... but alas, such is Destiny *cough* Grimoire *cough*