I've never really understood this advice. All computer hardware drops in price over time. If you wait long enough you can probably buy for $150 or less.
Most people buy quarterly or per occasion. For example, some people buy in anticipation for the start of a school year. Others buy in anticipation for a summer trip, and others buy for work. Most of these occasions can be broken down into quarters. Since the Haswell architecture is coming out at the end of the 3rd fiscal quarter, you can expect price drops on current architecture devices starting now, but peaking in the 4th fiscal quarter, which happens to align with social occasions such as summer vacation or the start of a new academic year.
Therefore, it's not about waiting "long enough". It's about making a smart purchase depending on when you need to make a purchase; if you're looking for a new device for the start of a school year, for vacation, for business, etc., then you can probably wait until July or August, which is the prime time to purchase a device such as this.
The more you know...