* Is it OK to check if Thermal Paste spread evenly? *

I allways do that. Seems to work for me.

well, some will claim never do that as it will get air bubbles in it and reduce the efficiency and even create hot spots in the surface which your temp sensor won't detect.

Some people are also full of crap so take that for what it is worth.

If it [TIM] has been on for any length of time you might have to reapply again,after all there should only be TIM to the thickness of a cigarette paper..

edit: If there are no problems,,why go looking for them,windoze don't need no help in that department..

I never check it...

I install the heatsink or waterblock and run coretemp or realtemp in windows to get my temps.
-If temps are awesome, I leave be...
-If temps are mediocre / terrible I remove the heatsink. All the thermal paste and start over… Rinse/repeat until satisfied I have a great connection.

Sometimes ill do this process three or four times per heatsink, but I always get the best temps in the end.

**edit**
***One thing you should note if you have not removed a heatsink before… warm up the processor/heatsink by leaving the machine on a few mins before trying to separate the processor/heatsink. When cold, they stick together like Bert and Ernie.