The only thing I dislike that is inherent to points of any kind is they're often not able to be turned back into money, so through gift cards or gift systems, or forced initial overtransfer, people are left with points they'll never cash in. Maybe they only wanted the one thing and had to convert more anyway to make a minimum amount. Deviant Points on dA are a particularly good example of a digital currency no-one wants to use. Artists now have the choice to offer commissions in Deviant Points, but what are they going to do with the points? The only thing they're used for is buying other commissions, dA merchandise and art from other people. Artists don't want points. Basically, I don't like points because they narrow your purchasing options irreversibly.
The other main thing I've seen mentioned is that there can be a minimum amount, ensuring you'll never use it all because you'll have 'change' left over, but this is common to proper money as well in many systems so it's not a problem concerning points. There's also the issue of strange conversion rates designed to f*** with you and distract you from the price of what you're buying, and that's probably got some merit to it as well.
The other main thing I've seen mentioned is that there can be a minimum amount, ensuring you'll never use it all because you'll have 'change' left over, but this is common to proper money as well in many systems so it's not a problem concerning points. There's also the issue of strange conversion rates designed to f*** with you and distract you from the price of what you're buying, and that's probably got some merit to it as well.