One of the nastier surprises I discovered when I switched to digital two years ago was the dreaded "crop factor" (APS-C / APS-H / DX / FX, four-thirds, etc.). If you’ve yet to buy a body and want a basic grounding in the pros and cons of each sensor format in purely photographic terms, I heartily recommend the Christmas issue (No. 93) of a UK publication, “Black and White Photography”, the article by Steve Hynes.
Below is the link to the publication, but the article hasn’t been posted on line. (BTW, this is not a plug for the publication. I have no link with it. I just found it very useful.)
I wish I had read this before I bought my first dSLR!