Engr, I developed projected income tax returns as part of my ER plan back in 2008 when ER was fast becoming a likely reality. Compared to my taxes when I was working, I first knew the FICA taxes would disappear completely. Next, I saw that my income tax bill would drop somewhat due to having my Qualified Dividends and LTCGs taxed at 0% federally. And finally, I saw that I would be deducting my individual health insurance premiums (above 7.5% of AGI; rising to 10%). This deduction has varied quite a bit in my 4+ years of ER because I have changed the HI company and my AGI has spiked one year, greatly raising the AGI to subtract from the premiums paid. I took the Standard Deduction in 2012 and will do so again in 2013.
In my years of ER, I reduced my holdings in muni bond funds because the gap between yield and tax-equivalent yield was shrinking. It is now preferable to go for the higher gross yield and pay the (lower) taxes.
Also, here in New York, they tax all investment income (i.e. Qualified Dividends and LTCG) at the same rate as ordinary income, so even though I am in the 6.645% bracket (starts at $20k for singles) I pay nearly as much in state income taxes as I do in federal income taxes, something which never happened when I was working. For 2012, only 62% of my income was subject to federal income taxes.
One last thing - I split my income taxes into two parts. One are the "basic" taxes on my more predictable income, mainly the monthly and quarterly dividends from my stock and bond funds. The second part are the "excess" taxes on my less predicable and more erratic income, mainly the cap gains distributions which may be large one year, small another year, and non-existent in a third year. I reason that if my income tax bill spikes one year, it will be due to the latter types of income, and I will always have the money to pay them from said erratic distributions.