Have you checked your ram usage? If you're maxing out it will slow to a crawl and it's faster to just kill it and reopen STS. If that's the case I found -Xmx840m to be the highest I could set it. To use more ram you have to Install STS on top of Eclipse 64bit.
Personally I have everything generated for about 60 tables, and the AspectJ builder is killing me. Not sure on the time difference, if I hadn't Refactored->Push-in, but right now AspectJ takes about 15 minutes, so make sure Build Auto is off. I plan on removing Roo support as soon as I'm sure everything has been generated properly and I think that will get rid of the build time problems.
I'm also using JDK 1.7. I have Eclipse running off the 64bit and my project using the 32bit since I read somewhere GWT needs it. I'm running the Roo 1.2.0.M1 since it uses GWT 2.4 and Roo 1.1.5 uses GWT 2.2.
On a side note if you use 1.2.0.M1/GWT 2.4 you'll need to change your pom.xml
replace the gwt-servlet dependency with: