Please don't wait. I'm usually not one to step on a soap-box to promote a product (steps down...) but this is a good one, one which many already know about and use.
I read a few bug reports and posts related to clearing out temporary ~/.evolution files, but this really never worked very well, as the issues always reappeared.
The last straw was not being able to expunge the Trash bin, and after a little bit of playing, decided I needed to migrate my mail to something else.
I figured since I already used Firefox, I might just as well take the Thunderbird plunge. Boy, was I glad I did! It was a snap using these directions, "How To Migrate From Evolution To Thunderbird In Ubuntu Intrepid" posted at MakeTechEasier.com.
I'm quickly finding there are more extensions available for Thunderbird than there was for Evolution.