I have finally upgraded to kubuntu 12.04 and with this, I also moved to KMM 4. First problem I get is that when I import an OFX file, all new payees (i.e. for which there is no match) are replaced by some gas station in Worcester, MA (which is an existing payee). I know there are/were some bugs in OFX import but I did not find this particular one. Is it a known issue?

BTW There is still a considerable speed disadvantage, e.g. in updating a ledger (entering or modifying a transaction) and especially in report generation.

I filed a bug for this, but the problem only occurs in a specific case and there is a workaround:

If the matching definition of a payee is set to "match on a name listed below" and the list is empty, this payee will always match. You an see this by running kmm in a terminal: it prints all matches found. This may or may not lead to an incorrect result in the ledger. If there is another match (not of the type match on list), the other match will prevail. If there are no other matches, an incorrect match may be retained instead of a new payee created. I found that if I swap the setting from "match on name listed below" to either of the other settings and back, the problem mysteriously disappears. That said, it does not make sense to match on an empty list, but I do not recall having changed this myself. No idea how it got that way.