This isn't really a bookmarks sync solution, but kind of a workaround.
You can store an HTML file called "bookmarks.html" on your dropbox. I leave it at the root level. Then you can edit it on the PC and add links.
On your Android phone, open up Dropbox, hold down your finger over the bookmarks.html filename and select "download" from the menu. Then in the default browser, go in and set the home page to:
file://sdcard/dropbox/bookmarks.html
Don't forget the "file://" part. This will make your home page in the browser your bookmarks file. If you make changes to it on the PC it will re-sync with Dropbox. You can also make changes to it on the Android (with something like text edit, etc.). Just remember if you use Text Edit you have to close the file (by opening a new blank file and saving bookmarks.txt) or the Android browser won't be able to load the page.
For those who don't know HTML, a sample line in the bookmarks file might read:
<p><a href="http://www.yahoo.com">Yahoo</a></p>