Welcome to WebmasterWorld Guest from 18.104.22.168
The toolbar is being used by someone browsing your site. That's why you're seeing the user's IP Address and not Google's IP Address.
As for why it's hitting your home page so often, perhaps someone is using Firefox with the auto-reload extension installed and has the refresh rate set to five minutes. I do that with several of my own websites all morning and evening except I use three minutes.
If it's a major annoyance there are ways of dealing with it. Let us know if that's the case please.
I suspect it's just what it says it is, Google Desktop, and perhaps the Web Clips RSS component has been cranked up to check your feed more often.
Just checked my log file, sure enough:
GET /rss_feed.xml HTTP/1.1" 200 11068 "-" "Mozilla/4.0 (compatible; Google Desktop)
And it's coming from a bunch of IPs