A number of SMP related issues were addressed here - crashing when entering certain servers, baby villagers only being farmers, and issues with spawning baby wolves, among others. Remember, if you aren't having trouble with 1.4.4, you can continue playing with it normally - however, if you want to update to the 1.4.5 PR client, don't fear! The 1.4.5 Pre-Release client should be able to connect to any 1.4.4 servers without any trouble at all.
Give it a try, see if it doesn't help with certain SMP issues! Whether it does or not, be sure to report your findings right here!
1.4.5 Client: Click here
1.4.5 Server: Click here