That question is really too vague to answer. It all depends on what you are shooting for. I'd suggest grabbing some videos off the web (if that is what you are encoding for) that are representative of your goals and checking out what they are using for compression meters. Either that or provide way more detail here.
No, 2MB is fine. For a one minute clip, I would say anything in the 480h range that is over 6MB may be overkill. 4MB is a good target. For 320h, 2-3MB is a good high ground, while 1-2MB is great if quality doesn't suffer significantly.