Currently, I do not put a limit on the features of the account. The only limits are space and bandwidth; otherwise they're able to use as many e-mail accounts and mySQL databases as they wish, as long as it is within their allocated space and bandwidth.
However, I will soon be changing this - Company image is everything really, and companies who offer unlimited features are not really looked upon as reliable by other companies, and even some people.
If you target individuals, then there is no problem offering unlimited features - they are very unlikely to actually use them all, and there really isn't a problem. What's more, they are then more likely to host with you. If you target businesses, then you really need to put limits on the features of each package; businesses do not think well of companies that offer unlimited features, unfortunately.
However - you could have two ranges of packages. One range for individuals which offers unlimited features, or a very large amount, and then a second range which is for businesses and there you offer limits of features on all packages.