Postcrossing has just updated the send limits for new users (or users with fewer than 100 postcards sent). You will now be able to send more postcards with fewer logged sent postcards. They can explain it better than I do, so I'll just quote directly from their post:
Today we are doing an update on the formula for limits in Postcrossing. From now onwards, the limit for new accounts will start to increase after the first 5 postcards sent (and registered). Afterwards, the number of postcards you can send will increase by 1 for each 10 postcards sent (it was for each 20, so it grows twice as fast!). After the first 35 postcards sent, it increases by 1 on each multiple of 50 postcards sent.
We know this might sound a little confusing, so we made a little graph to explain the difference between before and after. Here it is:
As you see, the limits grow faster initially, allowing the account to reach a more comfortable level sooner.
As for me, it's been a while since I've been able to have all my postcards traveling... I just don't have time to write them, and my current limit is 19. But all users get an extra postcard in their limit now, so in fact they just bumped me up to 20. It's a little holiday gift to everyone.