FirmTek announced the SeriTek/SpyderHUB, an interesting concept.

Thank to this enclosure, one can plug external SATA HDs (eSATA) to the SeriTek/SpyderHUB, then get the data through FireWire or USB2 when connecting the computer to the SeriTek/SpyderHUB. So, one can use eSATA with any Mac, even the Mac Book Air, or use those eSATA HDs as booting volume.
Of course the data transfer speed available will be defined by the slowest connection, so it will be far from being as fast as native eSATA. If such converters are also found in eSATA enclosures too, here FirmTek added an extra value by turning it into a multiport hub. With the SeriTek/SpyderHUB, one can even set external HDs as RAID 0, 1 and JBOD volumes. However, one will not be able to use external FireWire HDs and get the data via USB2; such additional features might have been useful for the MacBook Air.
The price of the SeriTek/SpyderHUB is currently not available yet.