I had the same problems after the n900 had an uptime of 2-3 days. The phone app would take far too long to load. I believe it was caused by the phone having to write to swap before freeing enough memory to load the phone application. I installed and used swapolube and phones running great! It make the more ram free and really improves the performance. Give it try, it eased a lot of my fustration with the phone.