One of the problems people may experience when trying out something like ZODB is trying to use it as they would use a relational database management system rather than as they would manage a normal object structure inside their program. Things like list comprehensions and careful design of the structure of the objects can improve things a lot, but I will agree that sometimes the fact that you can't as easily run ad hoc queries is sad. Also very often you simply won't need to use an index, and for a very large range of problems the graph nature of ZODB (compared with the tabular nature of the RDBMS, where you'll need indices to avoid full-table scans) is liberating.
Certainly there are some types of problems which ZODB won't work well with, but overall I quite enjoyed the experimental project I made early this year in Pyramid with ZODB. Combine it with traversal-based URL generation and you get very interesting results.
I think it's the sort of tool that I'd recommend people at least try; once they've broadened their horizons, then they can go back to using their RDBMS when they wish to. (In this it's just like Pyramid's traversal; many developers have forgotten that pattern matching is not the only good way of routing URLs.)
I've used Durus a lot (a simpler version of ZODB) and indexing was always the biggest issue I ran into. Normal object associations don't need traditional indexing but object lookup based on attribute values gets pretty painful without some indexing support.
Certainly there are some types of problems which ZODB won't work well with, but overall I quite enjoyed the experimental project I made early this year in Pyramid with ZODB. Combine it with traversal-based URL generation and you get very interesting results.
I think it's the sort of tool that I'd recommend people at least try; once they've broadened their horizons, then they can go back to using their RDBMS when they wish to. (In this it's just like Pyramid's traversal; many developers have forgotten that pattern matching is not the only good way of routing URLs.)