I've gotten questions from people over the years about long account numbers/lots of segments, so I thought I would put together a short list of the pitfalls of very large account numbers.
The longest GL account number I've worked with in GP is 27 digits, 8 segments. This is different from the account framework which may be large to accomodate changes but most companies have a much smaller chart of accounts.
When you have an account number of that size, some of the pitfalls in GP are:
1) You have to activate horizontal scroll bars in User Preferences and you end up scrolling left an right to see the entire account.
2) Many of GP's default reports aren't setup for accounts of that size and you'll need to modify posting reports for all modules and GL related reports.
3) You'll do a lot of resizing in Smartlists just to fit what you want on the screen.
4) You shouldn't see too many performance issues in GP but you may see serious slowdowns in FRx. This is especially true when using trees or reports with heavy account detail. Enterprise Reporting deals with large accounts and large datasets better, but the features are not identical between the two products.
5) Users will do a lot more searching on segments other than account number. Make sure you've got the other segments setup to be searchable in the account framework.