From PaidContent, who have counted
all the deals from Q1 '07 to Q2 '08 - interesting factoids are:
VC Investments:
-- Total number of investments:160
-- Total number of disclosed investments: 137 valued at $1,925,830,000
-- Average investment size: $14,057,153
-- Best estimated value of overall investment in the space (disclosed and undisclosed): $2,126,620,000
Acquisitions:
-- Total number of acquisitions: 100
-- Total number of disclosed acquisitions: 46 valued at $17,535,320,000
-- Average acquisition size: $327,313,415
-- Best estimated value of overall transaction in the space (disclosed and undisclosed): $20,594,510,000
However, given a few very high profile ones ( Google "merger" with Doubleclick at $3.1 bn, Microsoft buys Acquantive for c $6 bn - thats over half the total), the average sizes here are probably a bit misleading. Median / Mean may be better measures?