I had the same experience as you, but going from PR1.1 -> 1.2. Because the phone never retained factory config for very long, I always assumed that it was probably something I'd done that made it so much slower -- until I finally wanted to know for sure, by resetting it completely (firmware + mmc) and leaving it stock for a while.

I didn't go so far as to quantify system performance by running detailed analyses, but the UI simply felt laggy and appeared to be constantly running just beyond the point of maximum resource consumption where previously it felt smooth and performed without any notable slow-downs. In fact, I had used the email client and web feeds with PR1.1 but stopped using both completely (due to probably poorly implemented SQLite frequently corrupting the DB file it writes to, often ending up with many old entries that should have been deleted and a DB file that was nearing 100MB in size). In spite of this, the lag continued. And call me crazy, but I even think the reception has somehow diminished. Where previously I remember downloading an 80 MB media file at an average of 500 KB/sec via the mobile connection (5 Mbit/sec), now I'm lucky to see 200 KB/sec using my Wifi at home -- which itself has also degraded, to the point where the phone now frequently only sees 1-2 bars (previously: 4-5) of signal strength. Needless to say, I have kept the phone in pristine condition and actually managed to never drop it.

PR1.3 improved over 1.2 -- but only slightly. At this point I just wish I could go back to PR1.1; even if it meant having to forego whatever has been added in the interim. Because in the end, none of the presumed fixes and additions mean a thing when the trade-off is going from a functionally swift resource to a sluggish impediment.