Up until s60v5 WRT was basically useless. All you could do is web actions, fetch rss, most normal javascript type activities, but you could NOT access phone features like the call logs, location data, contacts, calendar, etc, etc. The list still isn't very long sadly, but you have to start somewhere.
The 5800 (and N97) have added all these functions which makes it much more interesting. Everyone on going on about how you program the palm pre with html+javascript+css, this is what WRT is. The widgets on the home screen of the N97 will have more power than in S60v3, and hopefully since it's good for something now we'll start seeing apps.