Thanks to Chris @ CSS-Tricks (for recommending the plugin), Slickhouse now has a 'Subscribe to comments' feature.
When replying to posts, simply tick the box below the Submit button that says "Notify me of followup comments via e-mail" and it'll do exactly as it says on the tin, well screen.
For those of you using WordPress you can get the plugin (currently version 2.1) from TxFx.net. To implement it is a doddle.