Don’t worry, none of the holes are critical, although a majority are rated “high” severity. Perhaps most noteworthy, Google has “prevented sandboxed processes from interfering with each other”, according to the security update. That’s probably a good thing, since the company touts its sandboxing as an important security feature of Chrome.
As Google explains in its Sandbox FAQ page: “The sandbox limits the severity of bugs in code running inside the sandbox. Such bugs cannot install persistent malware in the user's account (because writing to the filesystem is banned). Such bugs also cannot read and steal arbitrary files from the user's machine.” You certainly don't want any interference with that process.
Other "high" severity flaws plugged by Google in Chrome 20 include a number of use-after-free issues, such as in table section handling, counter layout, SVG resource handling, SVG painting, first-letter handling, and SVG reference handling, as well as problems with crashes in texture handling, integer overflow in PDFs, wild point in array value setting, uninitialized pointer in PDF image codec, buffer overflow in PDF JS API, integer overflow in Mastroska container, and integer overflows in lbxml.
Google paid out a hefty $11,500 in bug bounties for help with all of the fixes. Most of the bounties went to two researchers: $7,000 to “miaubiz” for help with seven bugs, and Juri Aedla with $4,000 for assistance with two bugs.