I've gone back-and-forth with whether or not to purchase real 3550 and 3560 switches for my home lab.  I've decided NOT to, and to continue for now with Etherswitch modules.  My reasoning for this is that I prefer renting racks for 8 hours to do real labs anyways, which allows me to switch up the rack configs and to force me to sit there and run a full lab non-stop.  So, since I'll be renting racks anyways, I'll just rent some time to practice switching stuff as well.  I also don't feel like spending so much extra time getting good deals on all the parts and re-configuring the lab.

Here's a list of the major features I'll be lacking with Dynamips, and they are significant:

• Cannot do ISL trunking
• Cannot enable bpdu-guard on interfaces
• Cannot do private VLANs
• Cannot do PAgP / LACP
• Cannot set switch ports to nonegotiate
• some optional available STP features, like bpduguard, bpdufilter
• MSTP
• layer 3 port-channel 
• Switch Database Templates
• udld
• port security
• port protected
• qos specific configuration of hardware queues like srr-queue
• extended VLANs, unless transparent

I'll still prefer to rent racks to get practice.  Luckily, http://www.gradedlabs.com is pretty cheap!