Even though last night's release is barely a proof-of-concept, 43 Things shows a huge amount of potential. If I were in charge over at Robot Coop, these are the 43 things I'd make sure were included with the final version of 43 Things:

Community:

1. Friends list
   
2. Friends of friends list (e.g.)
   
3. Similar users to you
   
4. Security for goals (public, private, friends only)
   
5. A blog for each user (or a separate blog for each user's goal)
   
6. A community blog for each goal
   
7. Plug-in for existing bloggers
   
8. meetup.org-style meatspace organizing (or integration with meetup)
   
9. Self policing ("This is a fake/obscene goal"), i.e. no more goatse
   
10. Reputation ("According to X users, I am an expert at this goal")
    
11. User profiles (like LJ or friendster)
    
12. "People goals" ("I'd like to befriend/sleep with/get hired by this user")
    

Personalization:

13. Goal similarities
    
14. Recommended goals
    
15. Goal tracking ("I'm not pursuing this goal, but I'd like to see what's happening with it")
    
16. Rate goals
    
17. "I've done this"
    
18. "I'm not interested in this goal"
    

Notification (RSS, email):

19. New goals matching a pattern or keyword
    
20. New goals from my friends
    
21. My goals
    
22. Most popular goals
    
23. Goal reminder emails
    

Productivity:

24. Calendar ("I will work on goal X this weekend")
    
25. Collaboration (like setting up an outlook meeting)
    
26. Productivity metrics ("You're on track to finish by...")
    
27. Comparative productivity ("You'll be the 6th user to finish...")
    
28. Research help (using google scholar)
    
29. Budget tracking
    
30. Inventory tracking
    

Zeitgeist/Superlatives:

31. Movers & Shakers
    
32. Most accomplished users
    
33. Users wet behind the ears
    
34. Busiest users
    
35. Most lackadaisical users
    
36. Most popular goals
    
37. Least popular goals
    
38. Highest rated goals
    
39. Most despised goals
    
40. Goals in the news (google news search)
    
41. Most talked about goals
    
42. Most accomplished goals
    
43. Most elusive goals