Shared Domain IPs, Recent Ranking Changes, etc.

I would love some sage advice here:

On sunday, I had a sight that was enjoying fantastic traffic (almost like 200 visitors/day up from like 5 or 10 since I started adding more content) have it's traffic start to plummet down to where it's 1 today. Also ALL the traffic to my other sites (that share links and IPs) have gone down.

I can't help but think/wonder if the drop in traffic to all sites is related.

Also, does doing alot of keyword research from one IP (and having a banned site that shares the IP with other site, even though I requested an inclusion) affect anything?

Basicaly I am wondering if I should:

-switch IP addresses of all domains
-get an anonymous surfing tool to do my keyword research.

Thanks alot in advance for the advice!

I would also like the answer to this since all my sights share the same ip. I am not doing anything crazy but it would be good to know so I can plan accordingly.

I think u r doing interlinking
IPs are imp but
most of the ppl use shared hosts
so many sites are hosted on them but still site ranks
google catches u when u do the interlinking between ur own sites on same IP
and specially when u do 2 way linking
so try changing the IP if u want to interlink sites