My main problem with it is the lack of enough fields to store all contact information. If you have, for example, a person's home phone number and mobile phone number, you end up using two entries instead of one, because last time I checked (and at least on the SIM cards I own) the storage format is a simple two-column list: Name-Phone. Furthermore, there are strict limits on the amount of characters one can insert (and the character set is very limited, too). Additionally, one can only store 250 entries or so (varies from card to card). To sum it up in one word, for me it's very unpractical. I remember having to use Bluetooth to transfer contacts from a old feature-phone to a new feature-phone because, obviously, the SIM card would not hold all the contact information I had in the old phone.
We certainly have the technology to make better cards with more storage (BTW, the space for SMS text storage on the cards I own is ridiculously small, too). But as people moved on to store information on "rich" contact systems and, more recently, in the cloud, I think there isn't much motivation to innovate in that area.
We certainly have the technology to make better cards with more storage (BTW, the space for SMS text storage on the cards I own is ridiculously small, too). But as people moved on to store information on "rich" contact systems and, more recently, in the cloud, I think there isn't much motivation to innovate in that area.