Puzzling Search Ranking Drop After New Skin on Site

[BBonanza]

We are having some search ranking issues which are puzzling us.
We have just launched a new skin on our website and our new site is now cached ok, but the issue is that some of our pages have disappeared from the index for some terms, not others.
For instance we have a page for widget1 - the page is cached by google but has disappeared for one term, but not another
e.g
used widget1 - gone - used to be 4th
second hand widget1 - 2nd - as it was before

The page is clearly ok, but gone for the top term and has now been gone for over 2 weeks.

Any ideas? this has happened on a lot of pages.
Funny thing is that the dynamic page which holds the data is the exact same page which has held its rankings for other terms like:

used widget2
used widget3
used widget4

Thanks for your help

[tedster]

It's possible that the timing is a concidence. Often, ranking problems for one word and not others hook into over-using the problem word in internal anchor text - and the threshold for how much ir too much gets recalculated at times.

[ecmedia]

Did you design the new skin or it is one of those free ones from the web? The free ones can have links to bad neighborhoods and some evil people may have even hidden links. That could hurt you really bad.

[BBonanza]

ecmedia we designed it ourselves so I think we are ok on that front, but tedster you may have a point because our pages use the word "used" heavily.
I will try cooling the page down with this word.
Thanks Guys