I think DALnet's
netiquette article sums up quite well:
"When you chat on the IRC, you adopt a nick (nickname) by which others will know you. Your nick is your first impression to those you meet, and it should be chosen wisely. Nicks which contain offensive words (we all know what those are) or relate to activities or opinions which should best be kept private, may be considered to be inappropriate in some channels.. It's best to choose something which reflects you, as opposed to a nick that is chosen for its shock value. Avoid spaces and unusual characters in your nick."
Offensive nicknames are usually a big no no (i.e. instant ban), but I find most channels are fairly relaxed about multicase nicknames/hard-to-read nicknames, but you're not setting yourself up for a good first impression.
Regards,