OK this is a bit of shameless cross promotion to my company however the solution is very cool.
John DeGiglio recently wrote a 2 part series on developing a web part for displaying a twitter feed in SharePoint 2010.
The links to the articles are here: part1 and part2
One of the issues that John discovered was that other web parts would swamp the number of calls to the Twitter API.
John’s solution includes a WCF service to throttle the number of requests.
And now the best thing, John has very kindly published this solution to codeplex.
Gavin's Sharepoint Blog 