Internet Explorer issues (only about 3.1%
You must mean IE 7. The numbers are much higher for 8 and 9. In any case, all of the below - most of my documents render fine in IE7 (and thank Bezeebus it's finally going away.)
1. VALIDATE. :-)
2. Everyone is jumping on the HTML5 bandwagon. I'm holding off. Why?
In the 90's we put a great deal of effort and frustration into browser identification and applied all sorts of hacks to get them all to play along. What most found out was that there was a better way; code your way out of situations where you'd need to "trick" browsers into playing along.
So today in emergent HTML5 documents we have stuff like this
<!doctype html>
<!--[if lt IE 7 ]> <html lang="en" class="no-js ie6"> <![endif]-->
<!--[if IE 7 ]> <html lang="en" class="no-js ie7"> <![endif]-->
<!--[if IE 8 ]> <html lang="en" class="no-js ie8"> <![endif]-->
<!--[if (gt IE 9)|!(IE)]><!--> <html lang="en" class="no-js"> <!--<![endif]-->
or this
<!doctype html>
<!--[if IEMobile 7]><html class="no-js iem7 oldie" itemscope itemtype="http://schema.org/Product"><![endif]--> <!--[if lt IE 7]><html class="no-js ie6 oldie" lang="en" itemscope itemtype="http://schema.org/Product"><![endif]--> <!--[if (IE 7)&!(IEMobile)]><html class="no-js ie7 oldie" lang="en" itemscope itemtype="http://schema.org/Product"><![endif]--> <!--[if (IE 8)&!(IEMobile)]><html class="no-js ie8 oldie" lang="en" itemscope itemtype="http://schema.org/Product"><![endif]-->
<!--[if gt IE 8]><!--><html class="no-js" lang="en" itemscope itemtype="http://schema.org/Product"><!--<![endif]-->
<!--[if (gte IE 9)|(gt IEMobile 7)]><!--><html class="no-js" lang="en" itemscope itemtype="http://schema.org/Product"><!--<![endif]-->
And I get a sickening feeling of deja vu, one that reminds me of the Great XHTML Bust. If you're easily swayed by terms like "MUST be cutting edge technology" and "forward thinking" and "take advantage of HTML5 technology," or are worried some competitor will come along and bash your work for being HTML 4 or XHTML, claiming "that's so last century," then be prepared for a lot of extra work, coding, and heavier documents involved in getting HTML 5 to work.
Take two documents. Do they render differently in HTML4 versus 5? No. An exception is if you NEED to use technologies in HTML 5, such as video without Flash.
If you don't require any specific HTML5 features, and your content is plain HTML, stick with HTML or even XHTML and validate it until the old browsers die out and the web is ready. Your valid (X)HTML documents will be very easy to convert to HTML5.
3. Code your way out of cross browser problems. I just ran across something the other day 'd never seen - a simple form was rendering weird in Chrome, the button was being pushed down an extra em. Even Internet Destroyer was playing along nicely. I found out the "user-agent style sheet" from Chrome was the cause. So I coded another way around it, without using hacks or conditionals. There is always a way if you let yourself see it.
4. Avoid hacks and conditionals. You can't ignore this one with HTML5. But with a validated (X)HTML approach, you can. Hacks and conditionals work, but there always exists the possibility that a future version will break your hacks, now you have to have a hack to fix the hack. It's nonsense. See #3: there is always a way.
That's how I see it, and it's working pretty well.