I recently learned about Vienna Ensemble Pro 6 (VEP6), which is commercial software that does everything NetVST does, and more. With the manufacturer's kind permission I tested the 30-day free trial version.
VEP6 is a bit expensive, but for professional users it will be well worth the price. It works very well, and can bridge between PCs, Macs, 32/64-bit, VST and AU in all combinations. Impressively, VSE has managed to reduce its CPU overhead to near-zero.
For non-professional users, the price may simply be too high. 275 Euro for the software itself, and then you need a USB dongle (either VSE's own or a Steinberg eLicenser Key) for every machine you want to use as a server. This brings the total price to about $400 USD, though VSE does sweeten the deal by including one license for their Epic Orchestra sample library and player.
Bottom line: If you're a professional composer, buy VEP6--it's excellent. If you're not a pro yet, but hope to become one, especially as a composer for film/TV where you'll need heavy-duty orchestra samples, think seriously about VEP6. Otherwise, use NetVST.