Summary: it seems the newer models lock into place a little easier but it is still recommended to support the motherboard from underneath while locking them down to avoid stressing/flexing the motherboard.
Pros: cheap with great performance; perfect for a general use computer that will rarely or never need to use high end production software/ high end 3d games.
Cons: the push to lock fastening system on the heatsink.
Summary: I have more 2nd and 3rd generation Pentiums out than any other processor. They work great, are priced right and just work and work. As we speak on my workstation I have open 5 Outlook windows, 5 or 6 Excel sheets, 8 pdf's, my CRM, our app specific billing and dispatch program, Thunderbird, and 18 internet explorer windows on 2 monitors. This is a typical workload on my Pentium, and as soon as someone calls in I will open a support session in logmein rescue.
Pros: Picked it up from newegg for $49.99. Awesome chip for the money! PDC G645 is setup in a MSI H61-E23 (B3) motherboard and acts as a file server, bittorrent server, web server, and does transcoding to my PS3 using the PS3 Media Server. Runs perfectly! It doesn't have hyperthreading, but when under load from the PS3 Media Server it is still super responsive.
Cons: Like one of the other posters said, if you understand the specs and how it will integrate into your hardware then there are no cons for this chip.
Summary: I have a ton of workstations running the 2nd and 3rd generation Intel processors, they all run great. I have way too many applications open all the time, while doing remote support for customers and it is like they are not even breathing hard. They run cool and quiet and just take what I throw at them. For the price, they are great.