As you may know from previous posts, such as my answer to the WoW Insider Community Topic 'Is leveling too easy?', I don't use heirloom items. It's a personal choice that I have made for myself. I didn't decide to not use heirlooms to be awkward or even as a sort of experiment - it just kinda happened. With time I guess it became more of a concious decision - I chose not to purchase heirlooms when leveling alts etc.
I jokingly call people within my guild cheats for using heirlooms and they joke about how long it takes me to level characters. This is without a doubt partially due to my lack of heirloom gear and the leveling boost they often give. But it is also related to my dilly-dallying about and un-streamlined way of playing the game. But that's how I like to play and level.
Having said this I have caved in a little! Last Sunday I came second in the Stranglethorn Fishing Extravaganza and having most of the prizes (including a number of High Test Eternium Fishing Line) I opted for the heirloom ring - Dead Pirate Ring. My druid now has it equipped and it's granting her the 5% xp increase from killing monster and completing quests. Granted, this isn't a massive boost but it's the first heriloom I've ever equipped and it will no doubt speed up my leveling, atleast a bit.
Despite having equipped this heirloom item I don't think it's the start of a slippery-slope. I can't see myself going a complete 180° and wearing full heirloom gear on all my leveling characters from now on. In fact, by the time I've got my druid leveled up I'll probably have forgotten I have the ring!!