I am a proponent for withdrawing your 401K. Here are my reasons:
1) Compare the ROI of you money even after penalties and taxes paid today. Run the numbers. In a decade you will be much better off. Utilize leverage and you 2x-3x your ROI. Also run the numbers with the stock market at 8%/year and your Real Estate portfolio at 10-25%.
2) The tax shelter aspect is good however you will have to pay taxes at some point. Really the 10% penalty is the only difference and this is quickly over come (2-7 years as mentioned in #1).
3) By having your money in a 401k you have it locked until you are old and at the mercy of the government who sets that age when you can touch it. Last time I checked many people were planning on retiring much earlier. Also I am speculating but I am sure that the government with engineer someway to get at people's retirement accounts.
4) If you are applying for loans you will need to boast your cash reserves since this is usually the limiting factor. Retirement accounts are seen as semi-liquid therefore you can only count it at 50-80% during underwriting.
5) Did I mention that 401k investment options suck and there are hidden fees in there.
6) The 2008 pullback was 7 years ago and market cycles typically are 8-12 years. My opinion as of 8/2015 is that the stock market (the world's ponzi scheme) has had some great gains over the past few years and statistics say a correction is coming. I am not a finance major but the stock index seems artificially inflated by an ok economy based on fictitious unemployment and inflation numbers and artificially held low interest rates. I don't know how the election or global instability play a role. Stocks/Mutual Funds are dictated by the stock price as a relationship or equation between the (1) company's strength/outlook and (2) the street's expectation. What makes you think your know (1) or (2) better than all the insiders trading on the floor? It is a 2 factor equation and per our teachings in algebra those equations are unsolvable.
Other notes:
-Bonehead alert: if your are going to withdraw money from your 401k please do not buy a boat, car, vacation, or any of the sort.
-The RothIRA is a good option because you can play that game where you can withdraw contributions at any time (not gains).