Which GB rom did you use? Because I tried CM7.2 and the problem is still there.
I used MIUI GB and Nik's Trinity 4.5/5.0
then I started using Nik's Aura v3, the keyboard lagged really bad that I have to start typing slowly
switched to IceCold, the problem was still there but it's better than the sense ROM. however the ROM was still not stable at that time, so I went back to Nik's aura with the same keyboard issue.
couldn't bear with it, I turned back to MIUI GB and it was just smooth...
missing ICS, I tried the Nik's aura again and it's still bad (silly me right? going back and forth)
at that time what i did was to use a compact style keyboard, depends on T9 to get the expected words.
Soon after, I tried the unofficial MIUI (based on icecold) and it was really smooth.
I just tried the official MIUI, unfortunately it's based on Sense.. so the lag was pretty bad