I'm interested to get people's opinions on Coinbase.com. I've seen varying reviews regarding Coinbase, but thought I would give it a try because of its "simplicity" and options for merchants. After waiting 5 days for my order to be processed, I got an email saying that my order had been canceled, which is apparently an old problem that hasn't been fixed. Other old problems seem to be not responding to emails or refunding canceled orders in a timely manner, but I cannot confirm or deny that since my order was only canceled this morning. They say they've raised over $6 million from investors, but apparently they haven't spent any of that on order processing or customer service.
Coinbase is GREAT once you have a Tier II account that does instant transactions. Don't have to worry about wire transfer fees or Dwolla delays or BitInstant being offline, etc.
The cancelled thing never happened to me but did happen to someone I know and it really sucked because the price of BTC was 15% higher 5 days later than when he bought. Once you get to Tier II that shouldn't happen though, and if it does you'll know instantly.