I’ve used Thunderbird to manage subscriptions as well, but I was already using Thunderbird for my e-mail. It’s more of a traditional subscription process. Each subscribed site is checked for new posts at regular pre-chosen intervals. You are notified when something is new, just like e-mail. Since my schedule tends to be a little erratic the regular interval updates tend to be annoying interruptions. For a less impatient person it would probably work well. They could choose a reasonable length interval and use it. It’s also conveniently a very nice e-mail program.