What's the difference between "FWIW" and "IMHO"?

• In my humble opinion (IMHO) underlines that the following is your personal opinion (as opposed, for example, to facts or to your company’s official position on an issue).
• For what it's worth (FWIW) is a disclaimer that your contribution to the debate might be considered marginal, i.e. that it may not address the heart of the problem, but you still find it has some applicability.

In short: no, they are not equivalent.

FTR:

Note that IMHO tends slightly to END a sentence, whereas FWIW tends slightly to BEGIN a sentence.

For example, that sentence could have "FWIW:" at the beginning of it.

On the other hand, that sentence could have IMO at the end of it.

Just FYI.