So far the ReelPortal software seems to be most usable on the Viewsonic G Tablet. The Samsung Galaxy Tab has a couple of major issues: can't access front camera, and poor performance. The first issue is common for Android 2.2 devices with dual cameras, because the OS doesn't support 2 cameras natively. However, Android 2.3 will have support, so it would be a non-issue once that's released. The poor performance is probably due to the single core, whereas the Viewsonic has a Tegra 2 dual-core CPU. The Viewsonic also has a single front camera, so it works for ReelPortal. Someone was able to do a 4-way video conference using the Viewsonic G Tablet and 3 PCs.
Link to Viewsonic thread: http://forum.xda-developers.com/showthread.php?t=908613
Remember to join room "xda" (all lower case) if you want to test with other xda members!