I am currently working on adding multi-currency support to the CMS which is one of the big ecommerce features that I've wanted to add for a long time. After a week or so of focusing on it I think I have a good implementation of multi-currency working well and will give a quick overview below of where we're at at the moment.
In the admin settings you set a main currency and default tax rate. You can also enable "other currencies" and set a default tax rate and a conversion rate for each of them. Tax rates are still editable on a product level of course but the defaults are pre-selected when adding a new product. The conversion rate for each currency allows the CMS to convert prices for other currencies automatically but you can also set product prices manually on a per product basis if preferred.
When adding/editing a product you set the main price in the main currency, which is pretty much how it currently works in the current release version. The product price is then converted automatically into the other currencies. When editing the product you can switch between automatic currency conversion and manual price entry for each currency. To accommodate all of this UI changes have been made to price section when adding/editing a product and to the Tax & Currencies settings page in the admin area.
On the front-end the customer can then choose their preferred currency from those that have been enabled. Product prices and the cart/checkout will update automatically to reflect the chosen currency.
Of course it is still possible to use just one main currency and not have any other currencies.
This is just a quick overview of what is to come if all goes well. Everything is subject to change and currently being tested. I might do a video or blog post with more details in the future once it has been tested sufficiently.