I hate to say this, but I might have found a flaw - and that's such a shame, because I want to do what you've done (which is to connect three external monitors to a Macbook).
Like you, I'm using a DVI adaptor to connect to my monitor to the Macbook (none of my monitors are native thunderbolt). The problem is that, technically, (and *please* correct me if I'm wrong), the adaptor is displayport to dvi, not thunderbolt to dvi (a thunderbolt port falls back to displayport if a displayport device is attached).
So, if we buy this device:
http://ca.startech.com/Cards-Adapter...on~TBDOCKHDPBC
It's worth reading the small print at the end:
"When using a single display, the dock lets you connect one HDMI, DisplayPort or Thunderbolt monitor. The Thunderbolt™ interface on the dock is backward compatible with Mini DisplayPort and when connected to a DisplayPort monitor, only a single display can be added as HDMI will be disabled. For dual display configurations, you can connect one HDMI monitor and one Thunderbolt monitor simultaneously."
So, as I read this, you could use the hub to connect a *thunderbolt* monitor and a second monitor (perhaps via HDMI->DVI), plus continue using your third USB Displaylink monitor. But I certainly couldn't afford an additional Thunderbolt monitor.
Now, perhaps there are hubs without this restriction? But I would be very wary if you're planning to attach monitors to the hub via DVI adaptors to the Thunderbolt ports.
Pah!