There are many reports from upset Google Toolbar users in the Google Web Search Help forums. The complaints all stem around the font size within the Google Toolbar.
Here is one of the complaints:
this large font is obnoxious. google please change it back or give us the option to do so if we want. pretty lame you didnt initially give us an option, let alone even a heads up.
Some of the users posted screen shots of this problem and here is one of those screen shots:
As you can see, the font size seems just a bit large for one's liking.
The thing is, Google is not fully aware of why this is happening.
Googler Kelly F. came into the thread and said:
This appears to be a hot topic! Thanks to all of you for coming to this forum to discuss it. Would you mind telling me which browsers and operating systems you're using? Any extensions or add-ons?
Shortly after, Googler Gwyneth B. came in asking for additional information. She asked, "It would also be really helpful if you all could provide screenshots of the enlarged font size you're experiencing."
So far, there is no solution posted in the forums. But if you have this issue, I'd check the thread throughout the day for updates.
Forum discussion at Google Web Search Help.