Just wanted to report back for future travellers. My boyfriend and I applied for our Vietnam visas in Hong Kong and it went smoothly. The office is located in Wan Chai on the 15th floor of the Great Smart Tower, 230 Wan Chai Road. There was some scaffolding around the entrance but we found it easily.
When we got to the office there was no line and grabbed two forms (located in the corner of the counter). Just uh...don't fill them out
at the counter like we started to do...there's a little waiting room outside.
Bring cash! We had to go find an ATM and when we got back there was a long line but the lady at the counter did hold our information/passports for us and the transaction was quick. We selected the 2 day proccessing and it cost 580HK/each for a single entry 30 day visa. There were options for a one day turn around and maybe even an express same-day but I do not recall the prices for those.
Two days later we returned in the morning and after a few minutes wait (a small line but seemed to be more pickups) we had our passports with nicely places visas attached!
** It says so on the form but think carefully when you want to enter the country. We had just gotten our Chinese visas and it gave us flexibility on when we could enter the country (anytime before our stay in Hong Kong was up) but the Vietnamese visas use the dates you provide on the form. I'm not sure if this is an anomaly or something. Luckily the boyfriend noticed this and we gave ourselves the the whole month.