I recently mixed up two batches of restore magicka potions. One batch came out at 0.10 lbs, the other at 0.03 lbs. What in the world would cause this? I might have selected frost salts for the first ingredient one time, and comberry the other?... I can't figure it out...

Funny you mention that, a bug with potion weight was recently brought up in the Morrowind Code Patch thread.

@Yeah_that_guy - Thanks, I read through the thread and saw all the potions posts. Very Interesting, it appears I'll need to wait until the dust settles on MCP 2.0.

All my potions weigh 0.75 to 1.5 pounds They take up like 100 lbs in my inventory..

since there are more than 1 ways of making any potion you will have to look at the weight of individual ingredients.

for example:

Ash yam and netch leather will make a fortify intelligence potion that is heavier (0.8) than a ash yam and bloat potion (0.3)