A good ERP system should be able to provide you with solid, measurable financial benefit, even in the first year. Customer satisfaction should measurably increase based on improved on-time delivery, increased quality, shortened delivery times, etc. Inventory carrying costs generally decrease substantially due to better planning, tracking and forecasting of requirements. Vendor pricing should decrease by taking better advantage of quantity breaks and tracking vendor performance.
Collections should be turned faster based on better visibility into accounts and fewer billing and/or delivery errors. In addition, there are many less tangible benefits, including a reduced time to close a fiscal period, more expedient data entry across the board, immediate management visibility into critical data elements, etc.
Please note that it is important to select and use the right system for your business in order to achieve the full benefits of ERP. This is no small task; be prepared to spend time determining your business needs and researching the appropriate solution, both from a feature/function and a technology standpoint.