We tried out using a sorte (tarot) deck instead of dice last night. I gave the players a choice of either using dice or cards. 3 chose cards and 2 stuck with dice.
We discussed the major arcana rules, and liked the look of them, but as they were incomplete we didn't use them.
The big effect we saw was how many court cards turned up it probably averaged to about 2 per 'roll', which broadly reduced the number of raises accumulated by one. Given the large number of raises players tend to generate, it didn't affect them too much, but it was at an obvious disadvantage compared to dice. I expected this and made it clear to players the likely cost should be offset by the benefit of the extra abilities the court cards offered.
The court cards abilities were interesting, but players often had several (up to 4 was the highest) abilities to look up and consider whilst also making raises. This did slow down the process compared to dice.
Afterwards we discussed the mechanic. It was well received but we thought it could be improved with a small tweak. Using the deck to replace the 'narration' dice (the dice you should get for saying something more interesting than, "I sword them to the face") seemed like an elegant solution. Each player draws a card rather than rolling a dice. If you draw a number it adds to your pool as normal. If you draw a court card, it doesn't skew your average raises too badly and you only have one ability to look up and consider. Linking it to the idea of narration also creates a narrative link - how does what you are doing cause the effect that the court card describes?
One example: during the duel, Alexsy was trying to whip up the crowd to support Ennio. He drew the King of swords - everyone takes enough damage to cause a dramatic wound. He narrated it that he was so effective at egging them on that a brawl erupted, explaining why everyone took dramatic wounds.
In summary, the players using the cards enjoyed the alternate mechanic and the extra options but the slow down this created wasn't worth the payoff.