Since we upgraded from Word 2002, ACT 2006 to Word 2007, ACT 2008 our contact merge has slowed dramatically. It used to take us a matter of minutes to merge 100 contacts into a Word letter, now it takes upward of 30 minutes. Even after the merge is complete, it takes a long time to "load the file."
The speed difference between earlier Act versions and the newer Act 2007-2008 was dramatic. I upgraded to a Pentium 4 Dell pc with 2 GB of ram and unfortunately ACT is still somewhat of a "pig". The merge shouldn't take 30 minutes though.