I was impressed with the ease of use and pretty pleased with the speeds. I didn't have to do anything special to get this work. Just followed the instructions in the Android 2.3 manual for the Nexus S. One hiccup: I did have to restart my laptop after untethering before I could get the connection back. Note: I'm getting HSPA instead of 3G most of the time.
Here are the speedtest.net stats:
Captivate as Wireless AP (phone connected to network HSPA but not WiFi)
download: 2.06 mbps
upload: 0.58 mbps
ping: 346
Captivate on WiFi tethered to PC
download: 9.06 mbps
upload: 2.46 mbps
ping: 43
Captivate on HSPA tethered to PC
download: 3.16 mbps
upload: 1.20 mbps
ping: 159
