Social map search + context lists
The first side effect of lists will be that people who follow a couple of hundred others can now follow many more - knowing that these 'check out their updates every once in a while' follows can be relegated to a list that doesn't clutter up the main feed. This will mean well-followed people/organisations will become even-more-followed people/organisations.
I'd also suggest that Twitter set up some default personal lists for each Twitter user that would define which sorts of updates they'd like to receive - what context they're in:
0. Family
1. Friends
2. Acquaintances/Facebook friends
3. Close colleagues
4. Co-workers/Superiors/Subordinates
5. Industry contacts
6. Work-related pundits
7. Entertainment/Pastime-based commenters and pundits
More thoughts on this at http://alex4d.wordpress.com