What's Karma For?
Orrian boxes, armor, crafting recipies for ascended, some cooking ingridients, cultural weapons…..
I would hold on to it right now if I were you. They are talking about karma vendors in the expansion and no telling what they sale and for how much karma.
ANet may give it to you.
here is a long list of everything you can purchase in the game using Karma.
http://wiki.guildwars2.com/wiki/List_of_karma_merchant_items
enjoy!
I’m not sure any of the Lion Arch vendors are there anymore. Which makes the wiki useless.
only LA has been revamped. that wiki page has a lot of information, 98% of it is accurate.
it’s kind of silly to discredit all the useful information because you found one thing wrong with it. you asked what karma can be used for, and there’s a comprehensive list.
basically any heart vendor, any purple icon over a merchant, or any temple will take your karma. try looking around in game, I’m sure you can find them.
Karma is a currency that you use at ‘karma vendors’ LA was revamped so it’s vendors are a little different but besides that to spend it look for the purple icon with the title ‘karma vendor’
If you have a lot of gold, there is also the “Karmic Converter” from a costly achievement which you can purchase one item from a random selection of three each day. Some of these items can be useful, such as Tomes of Knowledge and WvW supplies, as well as Obsidian Shards and T6 crafting materials.
And there is also the linen farm which converts karma into gold.
And finally, as previously mentioned, there will be new mastery vendors scattered across Tyria from which you can buy new and old items with karma.
“Linen Farming” looks good if I’m up the middle of the night and no one’s on to play Silverwastes. But I bet selling ecto from salvage of SW loot on a busy day, let alone if there is a chest run, will make me a lot more a lot quicker. So unless I get bored I’ll just let my karma sit and rot in my pouch.
Thx for all the answers! 
One quick way to get a fair return on karma is to buy orrian temple armour and to throw it into the mystic forge in groups of 4. The chances of pulling out valuable runes or armour items is reasonably good and its very quick, unlike all the messing about with cloth salvage.