First, cons:
-Every weaving spell consumes a huge amount of mana, requiring steps to be taken to not always be empty of mana (i.e. meditation, focus, MR and/or necro-forms)
-Without several other people available at all times to do a focus (or multiple accounts), weaving is mostly useless. With two people with two accounts, you can get a level 4 focus, which is acceptable. I have one account which leave me always looking for people to do a circle with.
Pros:
- Most weaving spells are extremely useful, especially with a high level focus. For example essence of wind will do a lot of cold damage to everything you can see if you have a level 5 or 6 focus. Add the extra penalties for fast cast or recovery with EoW and thunderstorm and you can have a devastating choke point attack. Nature's fury is good in all cases, but with a high focus it can be more powerful than an energy vortex (and you can have 5 of them). The only spells I really don't use on my weaver are summon imp and immolate weapon. The rest have good uses in my style of play.
-Weaving is limited to fast cast 4, which counters the slow cast time beautifully.