The only thing that worries me a little is some of the more esoteric features that 2950's support that the 2900XL's do not support or support slightly differently.

2900XL's don't handle port security in exactly the same way as 2950's or 2960's

If 2900XL's do Etherchannel, I've never seen it. I'm not even sure if plain 2950's do it and you may need 2950T or 2960's which do Etherchannel.

How big of an issue these 2 things are on exam day I would not know, and I would agree that to pass the CCNA exam it is probably more important to have a decent basic understanding of how STP works and VLANS & VTP function.

If you have a look at Scott Empson's excellent CCNA Command Quick Reference guides (both editions) you will quickly see that at least in the switching area, that 2900XL's do things differently to 2950's for some features and in other cases, there are features that you can't even do on 2900XL's that in theory a CCNA is supposed to be aware of.

Finally, when discussing 2900XL's typically we would be talking about WS-C2924XL-24 & WS-C2924XL-EN-24.

The 2924XL has a chassis that has a similar depth to a 3550 where as a 2924XL-EN has a chassis depth equivalent to most 2950's, and of course the 2924XL-EN obviously has more IOS features and will cost correspondingly more, although not that much more, say $20-$40 more.

Thanks for all your articles though Wendell, as it is a good exercise to keep evaluating my own lab as I work my way through the Certification jungle.