|since i will be using gentoo instead of ubunutu, am i going to be missing software that will only be availale in ubuntu?
This is going to sound a bit harsh here, don't take it personally please
You use Gentoo and haven't learned that if you can compile software for one distribution you can compile it for any distribution?
There isn't a such thing as software only availiable for Ubuntu if it is open source.
|also, why do some users of the same macbook report issues of heat and wifi problems while other don't?
This is a really good question to tell the truth. I think it has to come down to two things, one personal preference. Some people will be pickier about certain things.
But the second thing is that there are build issues and variances. For a while the Macbooks were known to have thermal grease installed properly, to much was used to the point it worked against each other, resulting in overheating problems. Likewise I am sure there has been problems with antenna placement on occasion.
Also, Linux tends to be slightly worse on the power saving, preferring performance slightly in that regards, so often you will find things running a bit hotter in Linux. Keep that in mind.
That being said, I personally haven't noticed any problems with my Macbook Pro myself in either of those two areas. I do recommend going ahead and picking up the extended warranty though as I have had enough issues pop up here and there I do think it is worth it for the laptops.