ahh, that was my post!
but anyway. what probably happened was somebody was hosting alot of malware using dropbox on their website, and googles bots downloaded it and tested it and it black listed the Domain. unlike other photo repositories, dropbox can host any type of file (but contained there in was only images)
anyway, that post is 100% safe
along with any other post contained on the site, the only reason you got the warning is because it was an image. and images download automatically that way you can see them. if it was a Link, you wouldn't have gotten the warning. and links cant be 100% safe. always have an active virus scanner up, and if you do not trust the source you downloaded any EXE or BAT or a few other extensions from, don't run it till you ran a scan on it (its free, there are even sites where you can upload it and it will scan it with 20 different scanners)
due to HTML being disabled on this forum (and most, and even if it was enabled it would still only allow formatting html to be entered like <b>) any thing that directly loads is safe, but links may be harmful.
Heed that advise on any website, especially those with user created content (like forums and blogs) and you will be safe.