It is said in the bitcoin wiki that:
The accounts code does not scale up to thousands of accounts with tens of thousands of transactions, because by-account (and by-account-by-time) indices are not implemented. So many operations (like computing an account balance) require accessing every wallet transaction.
so my question is, what solution would be acceptable to implement a program who would be in charge of thousands of account (like an e-wallet).
My first guess would be to run multiple bitcoind instances, in order to keep the account by daemon ratio under a certain limit.
Any other idea ?