I find that I'm limited to 8 VSTs. Is there a way of going around that limit?
How many can I load into the new SONAR?
 

Bounce the tracks and remove the plug-ins.
 
There are limits imposed in both MC7 and SONAR Home Studio.
A comparison chart for SONAR is here http://www.cakewalk.com/Documentation?product=SONAR&language=3&help=Comparison.html
 

yep... bounce or......
 
Upgrade to Sonar where you have the ability to load more VST's. 
 
You may be able to cross grade to something else that does support more VST's at a reduced price. That's how I ended up in Sonar.  They made me a no-brainer offer and here I am.

Thanks for the replies. I'll be looking into Sonar.

With Sonar, your limitation is in the computer.  How many things can the computer do at one time before it chokes?  With today's computers, it's quite a lot.  I've not been able to get mine to choke but I really haven't tried either. I just know that it runs everything I can throw at it without any issues.

Just a as a side note to add to what others have said, I have Sonar Platinum, and have 1990 VSTs.  (I have Waves Mercury as well as several other packages by other companies).  No issues at all.  I have sessions of over 60 tracks with 2 - 3 VSTs on each, and a Master track with 7 VSTs.