What does this matter? Well, some people will have amounts within their superannuation accounts that they can withdraw at any time. Called unrestricted, non-preserved amounts, I think these are generally undeducted contributions made into superannuation prior to 1999. (All contributions after then are preserved until retirement age). Currently, if you decide to withdraw an unrestricted, non-preserved amount you can nominate how much of the withdrawl is to be from the deducted and undeducted components of your superannuation account.
For example, of the $335,000 in my superannuation account, $55,000 is an unrestricted, non-preserved amount that I can withdraw at any time. My undeducted amount is $34,000, so under the current rules I can withdraw $34,000 as an unrestricted non-preserved amount and don't have to pay any tax on that amount. If I withdrew the maximum possible ($55,000) I'd have to pay some tax on the $21,000 "deducted" component (which was contributed into the fund out of pre-tax salary).
However, if I withdrew the same $34,000 unrestricted amount after the new rules come into force on 1 July, the amount would be treated as roughly 90% (34K out of 335K) "deducted" and only 10% "undeducted" - and I'd have to pay around 20% tax on the $31,000 undeducted component. So, withdrawing this $34,000 after 1 July would cost me an extra $6,000 or so in tax!
But wait, there's more...
Another other benefit of withdrawing $34,000 tax-free from my superannuation account before 1 July is that I could then use this amount over the next two years to replace around $48,500 of my taxable income (with a marginal tax rate of 30%), and I could therefore afford to salary sacrifice an extra $24,000 pa  into superannuation without reducing how much cash I have available to pay my bills. The benefit of doing this is two-fold. Firstly, the salary sacrificed amounts will only be taxed at the 15% superannuation contribution rate, rather than my expected marginal tax rate of 30% (which applies to income between $25K-$75K). The second benefit is that be doing this large salary sacrifice my taxable income should be reduced from around $55,000 to around $30,000 and I'll then be eligible to get a government co-contribution of up to $1,500 if I make a $1,000 undeducted contribution into my superannuation account.
Current Situation If salary sacrifice an
extra $24,000 pa
Taxable Income $55,000 $31,000
Salary Sacrifice $10,400 $34,400
SGL contribution $ 7,400 $ 7,400 
Income Tax due -$11,850 -$ 4,650
Super Tax due -$ 2,670 -$ 6,270
Super co-contrib $ nil  $ 1,300
(if make a $867 undeducted contribution)
Total after tax $58,280 $63,180
This means I'd end up with an extra $4,900 pa (tax saving and co-contribuction) by making the increased salary sacrifice. However, this is only possible as I have the extra $34,000 tax-free withdrawal from my superannuation account to supplement my income for the next two years. Otherwise my after-tax "take-home pay" would have been reduced from $43,150 to only $26,350.
By making these arrangements I'll end up with the following over the next two years:
Current Situation New Situation
Super Balance $335,000 $301,000 (withdraw $34,000)
Take-home pay $43,150 $31,000 (salary sacrifice)
Super withdraw nil $17,000 pa (split over 2 years)
Total cashflow $43,150 $48,000
Super contrib. $17,800 pa $43,100 pa
Super tax. -$ 2,670 pa -$ 6,270 pa 
Super balance $365,260 $374,660
after two years (ignoring earnings)
The only material impact of thisarrangement will be that the ratio of undeducted:deducted money in my superannuation account will be higher if I withdraw $34,000 of undeducted funds and recontribute via salary sacrifice (deducted funds). However, as all pension payments made from a superannuation account after you retire (and are over 60) are tax-free under the new "Simpler Super" rules, this shouldn't have any real effect in the long run.
 Under "Simpler Super" there will be an overall cap of $50K pa in deducted contributions - so you have to make sure your total of salary sacrifice and employer SGL amounts doesn't exceed this.
 My employer calculates the required 9% superannuation contribution levy based on my original salary (ie. before salary sacrifice is deducted). Legally it is possible for an employer to only contribute 9% of the actual salary paid (ie. after deducting the amount salary sacrificed). So it's important to check this with your employer before making salary sacrifice arrangements.
 The government superannuation co-contribution (up to $1500) is available on a 1.5:1 basis for undeducted contributions made into superannuation by employees with incomes up to $28,000. For incomes above $28,000 the maximum amount reduces until for incomes over $58,000 you're not eligible.
 There's no 15% contribution tax on the government co-contribution
DISCLAIMER: I'm not a financial planner, accountant, tax lawyer or in any position to give advice. This is just information about what I'm currently planning to do, and what I *think* the implications are. I checked my superannuation details (unrestricted non-preserved balance and undeducted component) with my superannuation fund, and I asked the Australian Tax Office "Simpler Super" help line about whether the new rules treating all withdrawals as being in the same undeducted:deducted ratio as the overall account would apply to unrestricted, non-preserved amounts. The ATO help line rep didn't know, and he had to go ask a "specialist" in this area to come back with the opinion that yes, this rule seemed to apply to all withdrawals by persons under age 60. As the ATO only gives binding private rulings about income tax questions and not superannuation, this seems about as definitive an answer as I can obtain. You could get professional advice from a financial planner, if so make sure that they really know the answer (since the ATO wasn't even sure!).