Regardless of your level in an agency, you always provide creative and strategic input to client campaigns. In-house, you're one step away from this creative process and can become increasingly distanced the further up you rise.
Sure, management, budgeting and internal reporting skills get more of a workout, but unless you work with agencies that can't think their way out of a paper bag, you lose out on an important part of what makes PR so exciting.
One reason I returned to agency life was the opportunity to marry client-side experience (understanding the reasons and motivations behind client decisions, appreciating their pressures) with the chance to think creatively again.
For many people, the perceived attractions of working in-house may be enough to move to the 'other side', but don't forget why you got into the business in the first place.
Charlie Coney, group account director, Launch Group.