For me, the big deal is NOT trying to keep up with changes in accounting! IMHO, duplicating the functionality of an accounting package can be like duplicating a database managing taxes - it changes often enough that you would be tethered, tied and chained to yearly updates.
Yes, there is the promise of work in the future, but wouldn't we all rather be tackling new challenges?!
I recently finished a massive 65-file (FM v6) solution for sales, purchasing, crm, communications, et al and have integrated it via Applescript with MYOB's Account Edge. My client does one daily data transfer (virtually down to a button click) and let's the scripting fly! The data is transfered from FM to MYOB first and then updates from MYOB to FM last.
The accounting program gets to do all the things it does so well and get updated as often as it wants. We, however, only need to manage the format of the data that we send to MYOB and the parsing of the data it spits out - BOTH of which we have complete control in FM.
Customer's extremely pleased to be able to maintain control of the process regardless of what the accounting package does in it's updates.