If you're an avid twitterer (or twit for short), you'll be very familiar with it's downtime issues. Well as I see it, there are 3 major problems Twitter has. Downtime, Spammers, and a lack of viable income.
So how do I think it can solve it's problems?
Simple, charge anyone with a follow to follower ratio greater than 2 to 1. This would immediately eliminate 99% of spammers, drastically cut the system resource issues (thus reducing downtime), and create an income for company. While I doubt this will completely resolve it's lack of income problem, it's a step in the right direction. Those who use twitter as a marketing method, can continue to use the service, but must pay for it.
That's my 2 cents.