Domains sharing DNS server and consecutive IPs

Is there a penalization for this situation?

[rubenbla]

I have two websites, hosted in the same ISP, with consecutive IP addresses and pointing to the same DNS server. The main search keyword is the name of the city this sites are about, one is about local news and the other is a tourist guide.

I've seen how one of the sites is going down on Google ranking for the main keyword, now in 5th page (from page 1), mantaining PR5, while sites before it have less PR and less number of backward links or even none at all. The other site is in 1st page for the main keyword.

Do you think this may be considered some kind of spam by Google?

[jeremy goodrich]

No, from what I understand, they would not consider that as spam. I've seen more than 50+ sites, all on the same server, same domain registration info, and all consecutive (or near enough) IP's, and all ranking well.

Some in DMOZ, some in Yahoo...

More than likely, your ranking fluctuations are the result of their testing and tweaking of their algorithm, as this last month's update seems to have changed a bunch of stuff around, while leaving other sites untouched.