[burpee]

I actually did something similar to this about 5 years ago with Flash. By applying a complex filter to a flat layer to make the layer behave and look like it was a liquid drop on a glass surface. Essentially I just embossed it with 4 different colors that matched the background and then added a subtle "gloss" on the top to give it a 3D experience.

The blobs merged together seamlessly when they even came close to eachother and were a pretty close impression of real liquid drops.

This technique might also work to make the merging of the blobs appear more realistic.