There is a significant different in performance between a 1.83 GHz and a 2.16 GHz MacBook Pro. The 2.16 GHz is 18 % faster than the 1.83. You won't see that for many operations but if you do things like compress video or you use Rosetta for PPC applications that aren't universal yet, you probably will notice the difference.
My price vs. performance breakdown goes like this:
1.83 (CTO 1GB RAM, 100 MB HDD) -> 2.0 (stock) is $200 and you get another 128 MB of video RAM too. This gets you a 9% improvement in performance.
1.83 (CTO 1GB RAM, 100 MB HDD) -> 2.16 (stock) is $500. This gets you an 18% improvement in performance and the additional video RAM.
2.0 (stock) -> 2.16 (stock) is $300. This gets you just an 8% improvement in speed.
1.83 (stock) -> 2.0 (stock) is $500.
1.83 (stock) -> 2.16 (stock) is $800
So, if you don't care about the extra memory, the larger HDD or the 256 MB video RAM, then the upgrade to a 2.0 or 2.16 GHz MBP is probably not worth it. But if the extras are something you were going to buy anyway or if you want the extra video RAM the decision is easier.
If you want the extras but are trying to save money, perhaps the 2.0 to 2.16 upgrade isn't a particular good deal in comparison to the 1.83 to 2.0 upgrade.
MacBook Pro 2.16 1 GB 100 GB 7200 RPM Mac OS X (10.4.5) Mac mini 1.42 1 GB; PowerMac 450 MHz (Upgd. 1.2 GHz)