It'll be cool if Thunderbird can be turned multi-process as more cores show up in everyone's CPUs, each tab in its own process such that when an email opens up and crashes, only that tab is lost, not the whole client. This would be dependent on the Electrolysis project for Firefox though..

I too would like multi-process Thunderbird. For, (1) Thunderbird does lag, at least on my old computer that has (nonetheless) a SSD and a quad-core (and quite a few AddOns), (2) multi-process Firefox is now going mainstream and showing the benefits it can bring.