Google's error report in webmaster tools tells me I have 774 404's. This is largely because of the way permalinks were setup in postnuke before I converted to wordpress. When planning the switch, I didn't realize that any post from my old site could be reached by /articles/postid/ (even if it wasn't in the articles category). This is because we had permalinks setup something like this /news/postid/ or /devotions/postid/.
Humans were linking to /news/postid while google was indexing /articles/postid/. So, in my transition, I mapped using the /devotions/postid/ format and so every devotion on my new wordpress site is a 404 now according to google (because /articles/postid/ will no longer reach my /devotions/postid/ like it did in the past.
Here's the kicker, I have a category called articles in my new blog (/articles/postid/), so right now, google gives me a 404 for anything not listed in my "articles" category.
I wasn't sweating it too much because I assumed google would rebuild my site index... but it apparently hasn't graced my site with its presence since April 3. I'm currently trying to figure out why not.