Traditionally, ABCL's CLOS implementation has been depicted as one of its weekest spots. The two main reasons being on one hand its speed and on the other the absense of a good MOP.
I'm proud to see that some of the improvements over the past year turn out to be real performance improvers. Ofcourse, there's more to wish for and improvements will keep coming in. However, another improvement of 90% as in the linked post... ?
As shown for a fact, ABCL's CLOS is improving and while possibly still it's weekest spot, it's definitely becoming useable. If you find performance issues, preferably with example code to show the issue, please report to the Armed Bear mailing list (address information on the project front page).
[Note added: Though 90% improvement is hard to achieve, another 30% (24 seconds to 16 seconds) were realised last weekend.]