Fanatic Cook has posted an excellent summary on the recent negative attention cast on garlic preparations, at least for LDL cholesterol reduction.
Go to http://fanaticcook.blogspot.com to view.
I think Fanatic Cook is right--despite the lack of LDL reducing effects, it doesn't necessarily mean no benefit whatsoever. Anti-coagulation and anti-inflammatory effects, in particular, are well proven.
I do think, however, that it argues more in favor of sticking to whole cloves, rather than supplements. The benefits are also likely small. I would view garlic as a soft advantage for your plaque control program. You can do fine without it. You might do slightly better with it.