First, Hari Raya Puasa (aka Eid al-Fitr, the last day of Ramadan) was on 28 July in 2014. Hari Raya Haji (aka Eid al-Adha, the festival commemorating Abraham's sacrifice and the climax of the Hajj pilgrimage) is an entirely separate and much smaller festival. "Hari Raya" alone usually refers to the first of these.
So in short, traveling around Hari Raya Puasa/Aidilfitri in Malaysia is best approximated as like traveling around Christmas in the West.
The eve of Hari Raya, or "virtual Christmas Eve", most companies have a half-day and everybody who possibly can heads out will balik kampung ("return to village") to join their families, parents, etc. This means massive congestion on main thoroughfares including the North-South Highway (Singapore-KL-Ipoh-Penang) and border crossings (esp. those from Singapore). Public transport will be sold out, buses and flights packed, etc, and you will have a tough time finding a rental car as well. Not a good time at all to travel if you can possibly avoid it.
Hari Raya itself is like virtual Christmas Day: most companies, attractions, restaurants, etc will be closed. However, hotels and core services (airports etc) of course stay open, as do some businesses that are owned by/cater to the Chinese and Indian communities. Also, unlike most strictly family-centric Western Christmas traditions, it's common for Malays to have open houses in the evening, where friends and acquaintances are invited to join the feast.
After the Hari Raya holiday (and any attached weekend) ends, the migration reverses, and the same roads etc are jammed again, only in the opposite direction.