Link is to the Bogleheads forum post where someone posted a link back in August. Before now, you had to call in to request the change, and it could take a few days, but now it's online and allegedly is done the next day.

I don't know when they added this, but I think it was sometime this year because I remember considering it last EOY (that's when I usually rebalance).

Here is a direct link, or you can get there on the website: Transact > Buy & Sell > Convert Vanguard mutual funds to ETFs. You can select either a number of shares or a percent of the total position.

As to why you may want to do this, here are a few reasons:

• converting shares classes isn't a taxable event (but you can't go ETF -> mutual fund)
• ETFs have a slighly lower ER (0.01-0.02% in most cases, so not huge)
• easier if you want to ACATS transfer shares to a different brokerage
• if you have a mix of ETFs and mutual funds, rebalancing between ETFs is easier, so moving a portion of your mutual funds to ETFs may be worthwhile

Have you taken advantage of Vanguard's mutual fund -> ETF conversion? Do you think you'll use this new online tool?