The effective date is a very useful piece of information. How it should be presented in the GUI is another question. Both dates could either be visible side by side in different columns or there could just be an option in the account view settings.
I am not sure if the effective date is included in OFX format (or other formats). But having the effective date in my gnucash file would be excellent. I could e.g. write a script that would just flip the dates in the gnucash file to have a different view on the transactions.

Any user undertands he bought one day, but pays only on the due date of his credit card invoice!

This solves too the problem posted as "Installment forcast or matureness": http://gnucash.uservoice.com/forums/101223-feature-request/suggestions/6058694-installment-forcast-or-matureness

I am not really sure if this is covered by book keeping. I also read the article in the gnu cash wiki http://wiki.gnucash.org/wiki/SoC2007#.22Effective_Date.22_for_transactions... but come to the same conclusion.

For book keeping there is only one date when the payment arrives. Even if it is paid before due. It comes balanced once the debt or other way round the receivable is booked.

For double book keeping, at least EU/DE style there is a difference between the payment made and the claim.
More simplified: receiving a payment does not mean you own it until there is the transaction that says you own it (for the books).

What Jonathan says in his comment is maybe a matter of cost calculating or calculatory cost distinction.

I book pays always with the month they are related but of course with the day they are actually paid. And also the date the debts become effective.
This makes it pretty clear what a certain clients history looks like even without report. I can immediately see the currently remaining debts etc. and easily see when a payment was missed out or which did not match the payroll.

To solve the other, that is the reporting issue the report could be generated by the receivables.

Tags could be asolution too.. but can a report group by tags?

Just to note, the 'tagging' request is at: http://gnucash.uservoice.com/forums/101223-feature-request/suggestions/1543027-transaction-classifications

I realise cstim has said it is unlikely, but I want to second this request. In the Business tab of Preferences, there is already a tickbox to 'Enable extra buttons', so why not an option here to enable Effective Dates (although it's more logical in the 'Accounting Period' tab)?

Derek Atkins mail about the requirements is very close to what I would like, although I'm looking at it from an Accruals accounting perspective, and would like to be able to generate a report of all transactions that are relevant to a particular period that are recorded outside that period.

In other words, I want an easy way to generate a list of 'Notes to the accounts' after creating the Trial Balance report so that I can be reminded of accruals and pre-payment adjustments that I have to make.

I don't particularly want the transactions automatically included in the calculations for their effective date, which would just mean that an entire pre-payment or accrual would be moved to the 'effective' period rather than flagging that I need to make adjustments for the transaction.

Maybe the 'tagging' request would solve all our problems, which would allow us to tag a transaction with the relevant period and then produce reports based on specific tags rather than actual dates.

It could be implemented as a feature that is disabled by default (i.e. hidden from the UI). The average user won't be bothered by it and I'll be able to accurately determine my account balance at any given time. If there is no effective date it could be assumed to be the transaction date.

I would personally like to see the effective date be an attribute for each end of the transaction, allowing for the different lines in a split to be effective on different dates. e.g. I get paid on the last weekday of each month. This transaction is initiated on that day and the deposit hits my checking account on the same day, but the deposit to my 403(b) account isn't effective for up to two weeks later. This is irritating when reconciling my 403(b) book because at the end of each quarter I'm entering fees and accrued earnings at appear to include my most recent contribution but actually don't.

I haven't looked at the code base but I am a developer and would be willing to try to help with this.

I'm afraid this won't be implemented simply because the User Interface for more than one date is most likely too confusing for the average user...