One of the reasons I heard not to use JetBrains ReSharper is its performance overhead. As a developer there is nothing more frustrating then having Visual Studio freeze and chock during coding.
JetBrains decided to address this problem and did some work recently released ReSharper 4.5 Beta version.
If you never tried ReSharper or tried using it and stopped because you couldn't stand the "complimentary" Visual Studio slowdown - get it now.