A recent article in Tech Crunch http://techcrunch.com/2015/05/16/bubble20/ reported that some worriers have started to worry that we are in a Tech Bubble because the Nasdaq has returned to the 5000 level where it was in 2000 before that bubble burst.
First of all, it amazes me that anyone would think that 5000 now would be in any way equivalent to 5000 fifteen years ago. Fifteen years ago! Figuring a normal growth rate for the market of, what? 7% growth per year? that current 5000 would be equivalent to a Nasdaq of 1812 in the year 2000. (The 7% may not be exactly accurate, but you get the point).
The Tech Crunch article points out the following little statistics:

The PE ratio of the Tech Sector during the dot com boom in 2000 was 152. Now it’s 27! (That alone should be enough to relieve your mind).

Price to book was 6.7  now it’s 3.9.

Growth / Time ratio was 19.9 – now it’s 2.4! (This is a calculation of the speed of growth of stock prices).
There are more interesting reassurances and interesting facts in the article.
Saul