I've only been using the Gravity Forms plugin for a few days but already couldn't live without it - a custom solution to achieve the same functionality would have taken days / weeks to produce!
I've tried other contact form plugins before, but none with this level of usability and some of the fastest support I've ever received!
The minor issues I've had have all been resolved, and the 1 major issue I had has a temporary solution in place with a full solution coming later this week in version 1.1
Thanks for all your support to get my forms sorted out, well worth paying for.
Examples of Gravity Forms in use: