I tried changing, well tested, a site i have that is on page 1 of google and yahoo for a few terms. I wanted to make the code cleaner with less table tags, etc and move the content higher up. Once, I did that the SERP dropped to page 2 of google.. my questions is, is that a temporary drop..? the content is all the same, navigation is better and some images with alt text were lost during the so-called upgraded design look, so I went back to original style and it went back to same position in yahoo and goog. what would you do, right now I am staying with, " if it ain´t broke don´t fix it concept especially since it is highin serps. I am asking this because I am designing all the other sites with main content higher in position vs nav thoughts..?
Did you check for other things that could have led to a drop - for example loss of certain links ? Wait for a while. Some fluctuations can occur in the SERP's-they come back to their original position after a short period
"what would you do, right now I am staying with, " if it ain´t broke don´t fix it concept especially since it is highin serps." If you think that the new design will make ppl stay longer on the site/buy something, so you should change. SERP will be back after a while.
some changes can really change your rankings.... but if thats really necessary, just continue optimizing your site to maintain rankings...
If you are sure your new code is correct and would make things easier for you or for your site visitors - go for it, the site would jump back to its rankings - to speed up the process, try getting a couple of authority links.
I've heard from programmers that cleaning the code has no significant effect on SERPs. Putting keywords on the start, in the title etc. helps though. Check the cleannes of code of some high positioned sites...all dirty.
On-page optimization does work. You need to just wait it out - if you've improved your site, then the SE's will follow soon. I did an on-page optimization that you might find interesting: http://www.googlewatchdog.info/2007/08/my-on-page-keyword-optimization.html ** watch those ALT tags - they might be more powerful than you think!