I'm not in the photography business, but I am part of the management team at a yacht club. We have about a $400,000 annual budget, roughly 350 members (customers) and a hundred or so suppliers. We moved from a lash-up in Access to Quickbooks last year and it is working well. I have some issues with the reporting features but I can usually get them to work once I've studied them for a while and pulled out half my hair! The basic invoicing and bill paying is excellent.
We haven't set up complex budgeting and modeling with the system yet, though it seems to have lots of capability. It is important that you structure your costs and expenses right if you want the advanced modeling tools to work.
I have found a couple of shortcomings, particulary in the area of batch billing. However, like Photoshop, there are many third-party software vendors that are very willing to sell you 'plug-ins' that will enhance the basic features with specialty functions.