I'm generally for Xandra Kitee's slow approach. It has taken time to grow our community to what it is. (Yes Xandra, we are on a dedicated server, we have plenty of bandwidth) Some interesting stats for you...
All traffic to the site accounts for 4- 7 Million hits per month.
The forums portion of the site accounts for less than half of all traffic.
We are averaging 6-10 new members daily. Most of these members tend to lurk and not to post right away.
We are generally very highly ranked by the search engines. At any given point during the day, there is at least one search spider on the site. (Googlebot, MSNbot, Lycosbot, etc)
The long term question that needs an answer is: What causes people to register... but then never post?