Mad Shrimps posted a comparison review between Core Duo vs Pentium M:

If you want an early taste of what Core 2 Duo will bring later this year, then the Yonah platform will surely be able to satisfy your curiosity, it offers an excellent power usage/performance ratio making it a prime candidate for small home theater PCs or a very silent desktop system. While the Dothan system was cheaper to build it's not sure how long it will be continued as the Core Duo is its successor.

Speaking of successors, the Yonah is also to be EOF in the not to far future, as Core 2 Duo for mobile CPUs is around the corner too, codename Merom it offers performance almost on par with Core 2 Duo for desktop. Luckily it will fit in some S479 motherboards you can buy today; the AOpen used here is one of them. How much faster will the Merom be? While there are no official benchmarks out yet, some lucky people have played around with them, this person compared Merom T7400 vs Yonah T2600 both are clocked at 2.16Ghz, the Merom comes out on top (to no surprise) but the difference is note worthy.

So at the end of the day, do we recommend 'upgrading' or switching to a mobile CPU for your desktop system? Only if you are impatient and you need a silent, cool, powerful system right now.