[Note: I somewhat foolishly composed my reply to your question in Taptivate's app "Spring" for iPhone and lost it all due to a crash while attempting to "send" (publish?) the answer. Attempt No. 02]
In many ways, success is like beauty—perhaps foremost, it’s in the eyes of the beholder.
Success is a difficult thing to judge in others; as everyone values different things, and what equates to success for one might equate to failure for another—let’s call him "two." One might want a wife and kids, and to live in a suburban area with good schools… while two might want a fast, luxurious car and a penthouse condo in a high-rise, living single with supermodel girlfriends.
People may value money, power, knowledge, love, fame, safety—but never all equally.
I see success as something best measured in bits and pieces. To acquire success in one thing often requires sacrificing something else. It’s unlikely that anyone is successful in all vital areas all of the time.
I think that if people achieve the true goals they set for themselves and progress—looking/thinking forward, that’s success. Happiness is important, too.
Often the more success you have, the harder it is to maintain. It’s easier to clean a puddle than it is to clean a swimming pool—and a swimming pool is far simpler than keeping a lake clean. Just look at Lake Merritt’s water and "coastline…" an example of some failure, that is.
I value to-do lists, journalizing and project management tools because they help to focus energy and keep things accountable. Success is a battle against entropy, and it isn’t always pretty. Sometimes attrition is unavoidable; it might be necessary to bite, scratch, bleed—crawl to the finish line… because the race can be brutal, with vicious competitors also seeking the same success.
In summary, success is about setting goals and reaching them while figuring out how to retain happiness and perpetuate the process.
[Another note: I'm glad I got to use Formspring.me—it'd be nice to do so more often. Hopefully more friends and pupils use it.]