Fix slow boot-up on Mac

Problem
Recently I ran into a frustrating issue on my new MacBook Pro Retina (with 512MB SSD). The time of (re)boot took a lot of time, holding the screen black for a long time.
I checked several tips, but it was not due to old hardware (...), also not that my disk was full (more than 50% free space).
I searched a lot and found a solution that works actually pretty well and seems really stupid to me (a kind of Microsoft-type-solution-when-something-unexpectedly-stop-working-well).

Solution
What you need to do is to go to System Preferences, and selecting Startup Disk. Then, select your primary disk, and hit ‘Restart’ from the same window.

That's all! It worked for me pretty well!
By the way, it seems that this happened after the update of OS X 10.10.3.

Time Machine - preparing to copy "forever"

Problem:
I just got a new HD in my iMac (HD replacement action of Apple). Got the latest MacOSX on it. So far so good, but placing back my data from my Time Machine backup disk, I ran into problems. I had first a message and sometimes errors, telling that my disk was not properly removed (however, that was done by the OS itself). I just restarted the computer and tried it again. I started with an action to place back some data (couple of MB's), just to try if everything was working well.
Well, it didn't. It was preparing to copy forever. And finder hang, couldn't shutdown the computer on the normal way. So, just hard reset...
Solution:
Due to the 'not properly removed' messages and errors, I decided to run the Disk Utility and from there I ran the 'Verify Disk' option on my Time Machine (TM) backup disk. This took about half an hour or so. The results it shown were all good (green messages).
But, guess what, after that, restoring data from my TM Backup worked fine. Depending on the amount of data I restored, it took just a little moment to 'prepare to copy' and then it started to place the data back on my computer just as aspected and with an appropriate speed!

iMac 27" internal speakers stopped working

Since two weeks, I have an iMac 27" (i5, 2,8GHz) at home. A really nice and beautifull machine for my photography and video hobby.
However, last weekend the internal speakers stopped working. Sometimes it worked after a reboot for about 5 minutes max, mostly less.
I searched around on the internet, but all kind of suggested tricks didn't work (like reset PRAM, plug and unplug a headphone, starting GarageBand and so on.
Today I contacted the apple support and they gave me the following trick to try. I share it with you, because this one I didn't found on the internet.

1. Shutdown the computer
2. Unplug the powercable
3. Keep the powerbutton pressed for 30 seconds. This will reset the SMC. This will in no way affect your data/installation. See also (http://support.apple.com/kb/HT3964)
4. Plug in the powercable
5. Start your iMac and here you are, all things are fine again (till now at least :) )

So, all credits to the Apple Helpdesk!
Edit: I just found this solution somewhere on the apple site. However, I didn't find it relating to my problem (I didn't search that well I suppose).