Is there another bubble in the tech sector?

Today the tech-heavy NASDAQ reached the 4000 mark for the first time since 2000. The Dow Jones, by the way, reached 16000 for the first time ever last week, far above it's all time high in 2007.

The rally in equities has been especially true in the tech sector, where with the exception of Apple and Cisco and a couple of other big players, stocks have been roaring. Facebook has doubled from it's lows early this year and above it's IPO price last year. Shares of Yelp, Zillow, Google, Pandora, Netflix, Hewlett Packard, OpenTable and Amazon among others have rocketed this year. Microsoft is closing in on $40 for the first time since the dot-com bubble.

Twitter nearly doubled in it's IPO. Biotechnology shares have been among the best performers this year, with already huge companies like Gilead and Celgene seeing 70%+ gains in their valuations. Even 3D printing companies have skyrocketed.

Qualcomm's lead in 4G phones, like it's near monopoly in EVDO a decade ago, is boding well. Alcatel-Lucent and Nokia are up huge on their 4G rollout businesses. Even electronics retailers like Best Buy and GameStop have seen their stocks more than double.

In my opinion, much of the appreciation in the tech sector is warranted, while some issues are just too pricey. For example, companies like Twitter and Netflix need to grow earnings at a breakneck pace without a hitch for years to come in order for their massively inflated prices to be warranted. While companies like Apple, Microsoft and Oracle shouldn't be this cheap.

The big difference this time, is that these companies actually have huge revenue growth and are actually spending cash wisely to grow. They have user bases and foundations to build on, unlike the dozens of companies of the dot com bubble who slapped ".com" on their company names and went public.

I don't see a bubble, just some opportunities to buy some internet stocks when Wall Street takes some of it's money off the table in the big names that have run up so much.

Thoughts?